'prehistorian' is formed from the prefix 'pre-' and the noun 'historian'. 'Pre-' originates from Latin 'prae' meaning 'before', and 'historian' derives from Greek 'historia' (via Latin 'historia' and Old French 'histoire') meaning 'investigation' or 'account'. The suffix '-ian' is an agent-forming suffix from Latin/French.

'pre-' + 'historic' (from French/Latin roots) produced 'prehistoric' in the 19th century; adding the agentive suffix '-ian' produced 'prehistorian', meaning 'one who studies prehistory'.

The components originally referred to 'before' ('pre-') and 'inquiry/account' ('history'). Over time the compound came to mean specifically 'a person who studies the period before written history'.