adverb
all; wholly; entirely; without exception
Dated adverb meaning 'all' or 'without exception'. Rare in modern Japanese; replaced by すべて, 全部, ことごとく, etc.
古い文献には「悉皆承知した」という表現が見られる。
In old documents, one can find the expression 'I have understood everything.'
The historical derivation is uncertain; the kanji 悉 (all, exhaust) and 皆 (all, everyone) combine to reinforce the meaning 'all'.