conjunction
and also; besides; on top of that
Adds an additional point, often with a nuance of 'and what's more' or 'and to make matters worse'. Used in informal speech and writing.
彼は遅刻した。さては、宿題も忘れてきた。
He was late. And on top of that, he forgot his homework.
interjection
so (I take it that...); so then; then...
Used when the speaker realizes or infers something, often with a tone of suspicion or sudden understanding. Common in spoken Japanese.
さては、またサボったな。
So, you skipped out again, didn't you?
さては、君が犯人だな。
So then, you're the culprit.
conjunction
Archaic conjunction meaning 'if that is the case' or 'then'. Not used in modern Japanese; replaced by それなら or だったら.
古文では「さては」を「それならば」の意味で使うことがある。
In classical Japanese, さては can be used to mean 'if so' or 'in that case'.