JLPT N3: ～きる ([do] completely; finish [doing])

First, you take the ます-stem of a VERB.

For example, 使う (つかう // to use) becomes 使います (つかいます // use), and then we chop off the ます to get the ます-stem: 使い- (つかい-).

Second, you add ～きる to the end of it.

Thus, we are able to say "(VERB) completely" or "finish (VERB-ing)."

V ます ＋ きる
completely VERB; finish VERB-ing

An example:

生まれて初めてマニキュアを使い切った。
うまれて　はじめて　マニキュア　を　つかいきった。
This is the first time in my life that I’ve used up an entire bottle of nail polish.
Literally: “am born (and) + for the first time + nail polish (=manicure) + を + completely used.”

Note that, as in the above sentence, we can use the kanji for 切る (きる // to cut). Using just the hiragana, ～きる, is fine, too.

Translations like "completely VERB" and "finish VERB-ing" aren't perfect. There is no simple English that matches up with ～きる, so translations vary a lot based on context. The important thing to note is that ～きる adds this nuance that "all" of something was done, that something was done "to the end," etc.

So in our above translation, 使い切った (つかいきった) is meaning something like "(completely) used up."

In our next example, ～きる attaches to 疲れる (つかれる // to get tired; to be exhausted):

バイトから帰ってきた弟は、いつも疲れきった顔をしている。
バイト　から　かえって　きた　おとうと　は、　いつも　つかれきった　かお　を　している。
Every time my (little) brother gets home from work, he looks completely drained of energy.
Literally: “(non-career) job + from + return home (and) + came + younger brother + は, + always + completely became exhausted + face + を + is doing.”

Why did I say that バイト (=アルバイト) means "(non-career) job" instead of "part-time job"? Well, we have a lesson on that: [NDL #19] - The 40-Hour Part-Time Job.

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When used in negative sentences, it is very common for ～きる to be used in the (negative) potential form, ～きれない (or きれません, きれなかった, きれませんでした, etc.).

Take this sentence, for instance:

物的証拠が見つかるまで、彼が犯人だとは言いきれない。
ぶってきしょうこ　が　みつかる　まで、　かれ　が　はんにん　だ　と　は　いいきれない。
Until some material evidence is found, we cannot say for sure that he is the criminal.
Literally: “material evidence / physical evidence + が + is found + until, + he + が + criminal + だ + と + は + cannot completely say / cannot definitively say.”

↑ Though quite common, you'll probably only see the ～きれる (i.e. potential form) usage on JLPT N2 and above, by the way.

One of our very first NDL's was actually on making sentences like this: [NDL #17] - I can't understand this fully.

In that lesson, I also talk about how Rei's uncle, to his family's amusement, often says わかりきらない (←not a word) when he wants to say that he doesn't fully understand something.

Anyway, here is one last example:

試験当日は、緊張で力を出しきれませんでした。
しけん　とうじつ　は、　きんちょう　で　ちから　を　だしきれません　でした。
On the day of the test, I was so nervous that I couldn’t perform to my full ability.
Literally: “exam / test + the day of / the appointed day + は, + nervousness / tension + で + power + を + could not fully put out.”

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On a scale of worthless to essential, I rate this grammar "useful." You would do well to get used to it.