英语词源字典 - 在线词源网站

seasonable (adj.)[seasonable 词源字典]: "suitable as to the time or season," late 14c., from season (n.) + -able. Related: Seasonably; seasonableness.[seasonable etymology, seasonable origin, 英语词源]
unseasonable (adj.): mid-15c., "inopportune," from un- (1) "not" + seasonable (adj.). In reference to weather, "not appropriate to the time of year," it is recorded from 1510s. Related: Unseasonably.