'excitant' originates from French, specifically the word 'excitant', ultimately from Latin 'excitans', present participle of 'excitare' where 'ex-' meant 'out' or 'forth' and 'citare' (from 'ciere') meant 'to set in motion/rouse'.

'excitare' in Latin produced the present participle 'excitans'; this passed into Old French/Modern French as 'excitant' and was borrowed into English with the sense of 'that which excites' (noun) or 'causing excitement' (adjective).

Initially it meant 'that which rouses or calls forth' in a physical or figurative sense; over time it specialized to mean 'a stimulant' or 'causing physiological/mental excitation' in modern usage.