'investigation' originates from Latin, specifically the word 'investigatio' (from the verb 'investigare'), where 'in-' meant 'in/into' (or used as an intensifier) and 'vestigare' meant 'to track or trace'.

'investigation' changed from Latin 'investigatio' into Old French/Medieval Latin forms and then entered Middle English as 'investigation', eventually becoming the modern English 'investigation' (and plural 'investigations').

Initially, it meant 'the act of tracking out or tracing' (a literal searching or tracking), but over time it evolved into its current broader meaning of 'a systematic inquiry or formal examination' used in legal, scientific, and general contexts.