-기- is the causative suffix for verb stems ending in ㄴ, ㅁ, or ㅅ. From 웃다 ("laugh") it builds 웃기다 ("make laugh, be funny"); from 벗다 ("take off") it builds 벗기다 ("take off / peel / undress someone"); from 남다 ("remain") it builds 남기다 ("leave [something] behind"). This is the last of the five "core" causative infixes (이/히/리/기 plus the 우/구/추 group), and it rounds out the consonant coverage: where the others handle vowels, ㄱ-class, and ㄹ, -기- takes the nasals and ㅅ. It also gives Korean one of its most-used colloquial words — 웃기다 in its slang sense of "hilarious / ridiculous."
How -기- builds a causative
Insert 기 between the stem and the ending: 남 + 기 + 다 → 남기다. The base verb's subject becomes the object of the new transitive verb.
음식을 남기지 마세요.
eumsigeul namgiji maseyo
Please don't leave food (uneaten).
Compare 음식이 남다 ("food remains, is left over") with 음식을 남기다 ("leave food behind"): the leftover food, subject in the base verb, becomes the object in the causative, and a new subject does the leaving. Conjugation is regular for a 기다-stem: present 남겨요 (namgyeoyo), past 남겼어요 (namgyeosseoyo).
The -기- inventory
| Base verb | Causative | Romanization | Meaning |
|---|---|---|---|
| 웃다 (laugh) | 웃기다 | utgida | make laugh; be funny |
| 벗다 (take off) | 벗기다 | beotgida | take off, undress, peel |
| 남다 (remain) | 남기다 | namgida | leave behind |
| 맡다 (take charge of) | 맡기다 | matgida | entrust, check in, drop off |
| 신다 (wear on feet) | 신기다 | singida | put shoes/socks on someone |
| 숨다 (hide, intr.) | 숨기다 | sumgida | hide something |
| 감다 (wash hair) | 감기다 | gamgida | wash someone's hair |
아이에게 신발을 신겼어요.
ai-ege sinbareul singyeosseoyo
I put shoes on the child.
가방을 카운터에 맡겼어요.
gabang-eul kaunteo-e matgyeosseoyo
I checked my bag at the counter.
사과 껍질을 벗겨 주세요.
sagwa kkeopjireul beotgyeo juseyo
Please peel the apple.
엄마가 아기 머리를 감겼어요.
eommaga agi meorireul gamgyeosseoyo
Mom washed the baby's hair.
A pronunciation note: because the base stems end in ㅅ or ㅌ (웃다, 벗다, 맡다), that final consonant neutralizes to [t] before 기 and the whole cluster tenses in speech — 웃기다 sounds like [욷끼다]. Revised Romanization does not write the tensification, so we keep 웃기다 = utgida, 벗기다 = beotgida, 맡기다 = matgida; the tense [끼] lives in the pronunciation, not the spelling.
남기다 and its base 남다: a workhorse pair
남다 ("remain, be left over") / 남기다 ("leave behind") is one of the highest-frequency transitive/intransitive pairs in the language, and worth drilling on its own. You leave food (남기다), leave a message (메시지를 남기다), leave a legacy — all with 남기다; what stays uses 남다.
궁금하면 댓글을 남겨 주세요.
gunggeumhamyeon daetgeureul namgyeo juseyo
If you're curious, leave a comment.
돈이 조금밖에 안 남았어요.
doni jogeumbakke an namasseoyo
I have only a little money left. (base 남다)
The transitive/intransitive pairs page collects 남다/남기다 alongside 숨다/숨기다 and the rest of this productive family.
웃기다: from "make laugh" to slang "hilarious"
웃기다 starts as the clean causative "make (someone) laugh, be funny":
그 코미디언은 항상 사람들을 웃겨요.
geu komidieoneun hangsang saramdeureul utgyeoyo
That comedian always makes people laugh.
But in casual speech it has drifted into an adjective-like exclamation meaning "hilarious," and — with a sarcastic edge — "ridiculous, absurd, laughable." This colloquial 웃기다 is everywhere in spoken Korean and K-drama dialogue.
그거 진짜 웃겨.
geugeo jinjja utgyeo
That's hilarious. (casual)
웃기지 마.
utgiji ma
Don't be ridiculous. / Give me a break. (dismissive)
So 웃기다 has effectively become two words sharing one shape: the transitive causative "make laugh," and the colloquial evaluative "(be) funny / ridiculous." Context and tone tell them apart. Learn the slang sense as its own item — it's one of the most useful conversational words on this page.
Why 기, and its limits
-기- pairs with ㄴ / ㅁ / ㅅ-final stems where the softer 기 sits comfortably. As with every causative suffix, though, the final consonant only suggests the choice — it does not force it, and you cannot generate -기- by analogy. The ㄱ-final "feed" is 먹이다 (이), never ×먹기다; the ㄹ-final "inform" is 알리다 (리), never ×알기다. The suffix is selected per verb and memorized, so treat the seven verbs above as a fixed list rather than a rule you apply. The suffix-selection page lays out the full picture; the previous suffix is -리-, and the next is the -우- group.
Common Mistakes
1. Applying -기- by analogy to the wrong stem. "Feed" is fixed to 이 (먹이다), not 기.
❌ 아기에게 밥을 먹겼어요.
Wrong suffix — 먹다 takes 이, giving 먹이다.
✅ 아기에게 밥을 먹였어요.
agiege babeul meogyeosseoyo
I fed the baby.
2. Using intransitive 남다 for a transitive "leave." Leaving food behind is 남기다.
❌ 음식을 남았어요.
Wrong — 남다 is 'be left over,' intransitive.
✅ 음식을 남겼어요.
eumsigeul namgyeosseoyo
I left food behind (uneaten).
3. Confusing 웃다 and 웃기다. 웃다 = laugh (you do it); 웃기다 = make laugh / be funny (you cause it).
❌ 그 사람 진짜 웃어.
geu saram jinjja useo
This says 'that person really laughs' — not 'is really funny.'
✅ 그 사람 진짜 웃겨.
geu saram jinjja utgyeo
That person is really funny. (casual)
4. Using 벗다 to undress someone else. 벗다 = take off one's own; 벗기다 = take off / peel from someone or something else.
❌ 아이 옷을 벗었어요.
ai oseul beoseosseoyo
Reads as 'I took off (my own) clothes' — wrong agent for undressing the child.
✅ 아이 옷을 벗겼어요.
ai oseul beotgyeosseoyo
I undressed the child.
5. Overusing the slang 웃기다 in formal contexts. In an email or a report, use 재미있다 / 우습다; save 웃겨 / 웃기지 마 for casual speech.
Key Takeaways
- -기- is the causative for ㄴ / ㅁ / ㅅ-final stems: 웃기다, 벗기다, 남기다, 맡기다, 신기다, 숨기다, 감기다.
- 남다 / 남기다 ("remain" / "leave behind") is a high-frequency intransitive/transitive pair — drill it.
- 웃기다 is both the causative "make laugh" and the colloquial "hilarious / ridiculous" (그거 웃겨, 웃기지 마) — the latter is informal.
- RR omits the tensification you hear: 웃기다 = utgida [욷끼다], 벗기다 = beotgida, 맡기다 = matgida.
- The suffix is memorized per verb — you can't generate -기- by analogy (feed stays 먹이다, not ×먹기다).
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- Morphological Causative -리-TOPIK 3 — The causative suffix -리- attaches to ㄹ-final stems — 울다 → 울리다 'make cry / ring', 살다 → 살리다 'save', 알다 → 알리다 'inform', 얼다 → 얼리다 'freeze something' — with many landing as a single English transitive verb, plus the 늘리다 / 늘이다 trap.
- Morphological Causative -우-TOPIK 3 — The causative suffix -우- attaches mostly to vowel-final stems — 깨다 → 깨우다 'wake', 자다 → 재우다 'put to sleep', 서다 → 세우다 'stand/stop/build/draw up', 타다 → 태우다 'give a ride/burn', 크다 → 키우다 'raise' — with several stems changing shape (자→재, 타→태) because they hide an old double causative.
- Which Verbs Take Which Suffix (and Why It Is Unpredictable)TOPIK 4 — The morphological causative is a closed, memorized set, not a productive rule: the stem-final consonant only hints at which of 이/히/리/기/우/구/추 a verb takes, many verbs have no suffix causative at all, and the safe default for any verb is the productive V-게 하다.
- Morphological Passive -기-TOPIK 3 — The passive suffix -기- attaches to transitive stems ending in ㄴ, ㅁ, ㅅ, or ㅊ — 안다 → 안기다 'be held', 쫓다 → 쫓기다 'be chased', 끊다 → 끊기다 'be cut off', 빼앗다 → 빼앗기다 'have something taken' — and often carries an adversative 'it happened to me' colouring.