'arrestee' is formed in English by adding the agent/object-making suffix '-ee' (from French/Old French '-é') to the verb 'arrest', meaning 'one who is arrested'.

'arrest' entered English from Old French 'arester' / 'arrest(er)', ultimately from Medieval/Latinized forms such as 'arrestare'; English later created 'arrestee' by attaching the suffix '-ee' to this verb.

Originally, the root verb meant 'to stop or detain'; the derived noun 'arrestee' later came to mean specifically 'a person who has been arrested'.