'trainee' originates from English, formed by adding the suffix '-ee' (from Anglo-French/French use) to the verb 'train'. The verb 'train' comes from Old French 'trainer', where 'trainer' meant 'to drag' or 'to pull.'

'trainee' developed in English by attaching the -ee suffix to 'train' (itself from Old French 'trainer' and ultimately Latin 'trahere'); the -ee pattern (from Anglo-French/French) produced nouns meaning 'one who is the recipient of an action', giving modern 'trainee'.

Initially the root (Old French 'trainer' / Latin 'trahere') meant 'to drag or pull', but over time 'train' acquired the sense 'to teach or instruct', and 'trainee' came to mean 'a person undergoing training'.