To declare or assert something definitively; to state with certainty and without hesitation.
彼はその結果が正しいと断言して言い切った。
He declared definitively that the results were correct.
その説明だけで安全だと言い切るのは早すぎる。
It's too early to say for sure that it's safe based only on that explanation.
専門家は今のデータだけでは結論を言い切れないと言った。
The expert said that one cannot conclusively state a conclusion based only on the current data.
To finish saying everything one wants to say; to complete an utterance or finish one's sentence.
彼女は長い説明を一気に言い切った後、席を立った。
After finishing her long explanation in one go, she stood up.
最後まで言い切ってから質問に答えたほうがいい。
It's better to finish what you were saying before answering questions.