means A person who is being taught the skills needed to do a particular job, usually while already nominally employed to do it.

from From 'train' plus the suffix '-ee' that marks the receiver of an action (as in 'employee' or 'addressee'). 'Train' itself comes through Old French 'trainer,' to drag or draw along, from a Latin root 'tragere/trahere' meaning to pull — the same tug that gives us 'tractor' and 'tract.' So a trainee is, quite literally, someone being drawn along behind, pulled toward competence by hands that already know the way.