From on- + set. Compare Old English onsettan (“to impose; oppress, bear down”). For semantic parallels for the meaning to assault, compare cognate Russian насе́сть pf (naséstʹ), наседа́ть impf (nasedátʹ).
释义（英文）
名词Noun
(medicine, countable) The initial phase of a disease or condition, in which symptoms first become apparent.