'after-Easter' originates from English, specifically the compound of 'after' and 'Easter', where 'after' comes from Old English 'æfter' meaning 'following' and 'Easter' comes from Old English 'Ēastre' (also attested as 'Ēostre') referring to the Christian festival (and originally a Germanic spring goddess name).

'after-Easter' was formed in Modern English from the longstanding English words 'after' (from Old English 'æfter') and 'Easter' (from Old English 'Ēastre'), both of which passed through Middle English forms before becoming the present compound.

Initially the components meant 'following' (for 'after') and the name of the festival 'Easter'; over time they combined in Modern English to denote 'occurring after the festival of Easter'.