Verb (5-dan, る, transitive)
1. to declare; to assert; to state definitively
それだけは言い切れる。That much I can state definitively.
2. to finish saying; to say everything; to tell all; to finish one's sentence
彼はそれでどうやら、言いたいことを言い切ったらしい。And so, it seems he had said everything he wanted to say.