नहीं तो (nahiin to)

conjunction/particle A fixed connective meaning 'otherwise' or 'or else' -- literally 'not then' -- used to warn of a consequence if a condition isn't met. Related to नहीं (nahiin, 'no/not') and तो (to, 'then'), but functions as its own frozen unit.
Sense 1 : otherwise / or else (consequence warning)
conjunction Joins two clauses where the second states what happens if the first (often an implicit command or requirement) isn't followed: जल्दी करो, नहीं तो बस छूट जाएगी (jaldii karo, nahiin to bas chhoot jaaegii, 'hurry up, otherwise the bus will be missed').
Synonyms: वरना (varnaa)
Frequency: high
Cultural Note: You'll hear this constantly from parents, teachers, and shopkeepers alike -- it's the classic shape of a Hindi warning: do X, नहीं तो (nahiin to) Y (bad thing) happens. वरना (varnaa) is a near-perfect synonym and the two are used interchangeably in casual speech; नहीं तो (nahiin to) feels a shade more conversational to my ear.
Common Mistakes: 1) Learners sometimes try to translate this word-for-word as 'no then', missing that as a fixed unit it means 'otherwise' -- the individual pieces नहीं (nahiin) and तो (to) don't need to be parsed separately once you know the phrase. 2) It comes second, after the instruction or condition, never first: डरो नहीं, नहीं तो गिर जाओगे (daro nahiin, nahiin to gir jaaoge, 'don't be afraid, otherwise you'll fall') -- not placed before the warning.
Sample Sentences:
जल्दी चलो, नहीं तो बस छूट जाएगी। Hurry up, otherwise we'll miss the bus.
(jaldii chalo, nahiin to bas chhoot jaaegii।)
Register: Casual -- Mood: Imperative -- Voice: Active
खाना खा लो, नहीं तो ठंडा हो जाएगा। Eat your food, otherwise it will get cold.
(khaanaa khaa lo, nahiin to thandaa ho jaaegaa।)
Register: Casual -- Mood: Imperative -- Voice: Active
उसने छत्री ले ली, नहीं तो वह भीग जाता। He took an umbrella, otherwise he would have gotten soaked.
(usne chhatrii le lii, nahiin to vah bhiig jaataa।)
Register: Neutral -- Mood: Counterfactual -- Aspect: Perfective -- Voice: Active
समय पर दवा लेते रहो, नहीं तो तबीयत फिर बिगड़ सकती है। Keep taking the medicine on time, otherwise your health might get worse again.
(samay par davaa lete raho, nahiin to tabiiyat phir bigad saktii hai।)
Register: Neutral -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
साहब, कागज़ात पूरे कर दीजिए, नहीं तो फ़ाइल आगे नहीं बढ़ेगी। Sir, please complete the documents, otherwise the file won't move forward.
(saahab, kaagzaat poore kar diijie, nahiin to faail aage nahiin badhegii।)
Register: Formal -- Mood: Indicative -- Tense: Future -- Voice: Active
अगर तुम मेहनत नहीं करते, नहीं तो नतीजा अच्छा नहीं होता। If you hadn't worked hard, otherwise the result wouldn't have been good.
(agar tum mehnat nahiin karte, nahiin to natiijaa achchhaa nahiin hotaa।)
Register: Neutral -- Mood: Counterfactual -- Aspect: Habitual -- Voice: Active
दरवाज़ा बंद कर दो, नहीं तो मच्छर घर में आ जाएँगे। Close the door, otherwise mosquitoes will get into the house.
(darvaazaa band kar do, nahiin to machchhar ghar men aa jaaenge।)
Register: Casual -- Mood: Imperative -- Voice: Active
बच्चों को समझाया गया कि सड़क पार करते समय ध्यान रखें, नहीं तो कोई हादसा हो सकता है। The children were told to be careful while crossing the road, otherwise an accident could happen.
(bachchon ko samjhaayaa gayaa ki sadak paar karte samay dhyaan rakhen, nahiin to koii haadsaa ho saktaa hai।)
Register: Formal -- Mood: Subjunctive -- Tense: Present -- Voice: Passive
किराया आज ही चुका दो, नहीं तो मकान मालिक नाराज़ हो जाएगा। Pay the rent today itself, otherwise the landlord will get angry.
(kiraayaa aaj hii chukaa do, nahiin to makaan maalik naaraaz ho jaaegaa।)
Register: Casual -- Mood: Imperative -- Voice: Active
अपनी सेहत का ख़याल रखिए, नहीं तो बुढ़ापे में परेशानी होगी। Take care of your health, otherwise you'll face trouble in old age.
(apnii sehat kaa khayaal rakhie, nahiin to budhaape men pareshaanii hogii।)
Register: Formal -- Mood: Indicative -- Tense: Future -- Voice: Active
वह जल्दी सो जाया करता था, नहीं तो सुबह उठने में देर हो जाती थी। He used to sleep early, otherwise he would be late waking up in the morning.
(vah jaldii so jaayaa kartaa thaa, nahiin to subah uthne men der ho jaatii thii।)
Register: Neutral -- Mood: Indicative -- Aspect: Habitual -- Tense: Past -- Voice: Active
Sense 2 : or, alternatively (offering a choice)
particle Used at the end of a suggestion to offer an alternative, softer than a strict warning: चाय पी लो, नहीं तो कॉफ़ी बना दूँ? (chaay pii lo, nahiin to kofii banaa doon?, 'have some tea, or else should I make coffee?').
Synonyms: या (yaa)
Frequency: medium
Cultural Note: This is the same phrase softened into a hostess's or friend's offer rather than a threat -- context and tone of voice do the work of telling you which flavor of नहीं तो (nahiin to) you're hearing.
Sample Sentences:
चाय पीएँगे, नहीं तो कॉफ़ी मंगवा दूँ? Will you have tea, or should I get coffee ordered instead?
(chaay piienge, nahiin to kofii mangvaa doon?)
Register: Casual -- Mood: Subjunctive -- Tense: Future -- Voice: Active
पिज़्ज़ा मंगवा लेते हैं, नहीं तो बर्गर भी ठीक है। Let's order pizza, or a burger is fine too.
(pizzaa mangvaa lete hain, nahiin to bargar bhii thiik hai।)
Register: Casual -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
आप यहाँ बैठ जाइए, नहीं तो बाहर वाली कुर्सी भी अच्छी है। Please sit here, or the chair outside is nice too.
(aap yahaan baith jaaie, nahiin to baahar vaalii kursii bhii achchhii hai।)
Register: Formal -- Mood: Imperative -- Voice: Active
मीठे में गुलाब जामुन बनवाया है, नहीं तो हलवा भी है। For dessert I've had gulab jamun made, or there's also halwa.
(miithe men gulaab jaamun banvaayaa hai, nahiin to halvaa bhii hai।)
Register: Neutral -- Mood: Indicative -- Aspect: Perfective -- Tense: Past -- Voice: Active
फ़िल्म देखने चलें, नहीं तो घर पर ही कोई गेम खेल लेते हैं। Let's go watch a movie, or we could just play some game at home.
(film dekhne chalen, nahiin to ghar par hii koii gem khel lete hain।)
Register: Casual -- Mood: Subjunctive -- Voice: Active
अगर वो साड़ी पसंद न आए, नहीं तो हम दूसरी दिखा देते हैं। If you don't like that sari, or else we can show you another one.
(agar vo saadii pasand n aae, nahiin to ham doosrii dikhaa dete hain।)
Register: Neutral -- Mood: Subjunctive -- Aspect: Habitual -- Tense: Present -- Voice: Active
क्या आप कल आएँगे, नहीं तो परसों भी चलेगा। Will you come tomorrow, or the day after would also work?
(kyaa aap kal aaenge, nahiin to parson bhii chalegaa।)
Register: Formal -- Mood: Indicative -- Tense: Future -- Voice: Active
थोड़ा और रुक जाओ, नहीं तो अभी निकल भी सकते हो, जैसी तुम्हारी मर्ज़ी। Stay a bit longer, or you can leave right now too, whatever you prefer.
(thodaa aur ruk jaao, nahiin to abhii nikal bhii sakte ho, jaisii tumhaarii marzii।)
Register: Casual -- Mood: Imperative -- Voice: Active
अगर समय होता, नहीं तो हम बाज़ार भी घूम आते। If there were time, or else we could have taken a walk through the market too.
(agar samay hotaa, nahiin to ham baazaar bhii ghoom aate।)
Register: Neutral -- Mood: Counterfactual -- Aspect: Habitual -- Voice: Active