〜きる／〜きれない
Do completely to the end / unable to finishmachine translation
FormationVerb ます-form (drop ます) + きる・きれる・きれない
〜きる (written with the kanji 切る) attaches to a verb to express doing something completely, through to the very end: 読みきる (read all the way through), 走りきる (run the whole distance). The negative potential form 〜きれない means "too much/too big to finish": 食べきれない (can't eat it all), 数えきれない (too many to count).
Beyond completion, きる also expresses a state at its extreme: 疲れきっている (utterly exhausted), 信じきっている (trusting completely). The word 売り切れ (sold out) that you often see in shops is this very pattern in noun form.
Distinguish it from 〜てしまう (N4): てしまう says "finished doing" with a nuance of completion or regret, while きる emphasizes the will to do the full 100% without giving up midway — マラソンを走りきった evokes pushing on all the way to the finish line. The opposite of きる is 〜かける (leaving something half-done).
Examples
長い小説をやっと読みきりました。
I finally finished reading that long novel.
料理が多すぎて、一人では食べきれません。
There's too much food — I can't eat it all by myself.
マラソンを最後まで走りきった。
I ran the marathon all the way to the finish line.