'sporadically-employed' is a modern English compound formed from the adverb 'sporadically' and the past participle 'employed'. 'sporadically' derives from 'sporadic' + '-ally'; 'sporadic' originates from Greek 'sporadikos' (from 'spora' meaning 'scattering'). 'employed' is the past participle of 'employ', which comes from Old French 'employer'.

'sporadic' passed into English via Latin/Medieval Latin and Old French as 'sporadicus'/'sporadique' and became 'sporadic' in Modern English; 'employ' came into Middle English from Old French 'employer' (Modern French 'employer'), and its past participle 'employed' has been used in English since Middle English. The compound phrase 'sporadically-employed' is a modern descriptive formation combining these elements.

Individually, 'sporadic' originally related to 'scattered' (from Greek) and came to mean 'occurring at irregular intervals'; 'employ' originally meant 'to use or put to work'. Together the compound evolved to mean 'working or hired at irregular intervals' (i.e., not in continuous employment).