Trenchantly is the adverb from trenchant. It says that someone spoke, wrote, argued, or observed in a way that was sharp, direct, and to the point, with no cushioning to spare people's feelings — and, importantly, that they were right. 'He wrote trenchantly about the failures of the scheme' means the writing cut straight to what had gone wrong. You will nearly always find it attached to verbs of saying and writing: argue, observe, comment, put it, criticise. Like the adjective, it is formal and written; it lives in reviews, editorials, and serious essays, and would sound very odd in a chat with friends. It also keeps the adjective's approving tone. If you want to say someone spoke sharply in a way that only hurt, use 'harshly' or 'bluntly' instead — trenchantly carries the extra claim that the sharp words landed on the truth.

一針見血地、犀利地 (形容說話或寫作直指要害)。正式書面語，帶肯定的語氣