〜きる: do completely; to the end

Attached to a verb stem to say the action is done completely, to the very end, or to the limit.

Verb stem (ます-stem) + きる. 食べきる (eat it all), 走りきる (run the whole way), 守りきる (protect to the end). Often with 疲れきる, 信じきる. Negative 〜きれない = cannot finish / cannot fully.