'unexcitable' originates from the negative prefix 'un-' (Old English) combined with 'excitable', ultimately from Latin 'excitare', where 'ex-' meant 'out' and 'citare' (from 'ciere') meant 'to put in motion'.

'excite' changed from Latin 'excitare' to Old French 'exciter' and Middle English forms such as 'exciten', eventually becoming modern English 'excite'; 'excitable' was formed by adding the adjectival suffix '-able', and the negative prefix 'un-' produced 'unexcitable'.

Initially related words meant 'to rouse or arouse' (Latin 'excitare'), but the derived adjective 'unexcitable' evolved to mean 'not easily aroused or agitated' in modern English.