'regularly-hired' is a compound formed from 'regularly' and 'hired'. 'regularly' originates from Latin, specifically the word 'regularis', where 'regula' meant 'rule'. 'hired' originates from Old English, specifically the verb 'hȳran' (or Middle English 'hiren'), meaning 'to employ' or 'to give wages.'

'regularly' changed from Latin 'regula' → Medieval Latin 'regularis' → Middle English 'regular' and then took the adverbial suffix '-ly' to become 'regularly'. 'hired' developed from Old English 'hȳran' through Middle English 'hiren' to modern English 'hire' and its past participle 'hired'. The modern compound reflects a straightforward joining of these forms.

Initially 'regularly' meant 'according to rule' and 'hire' originally meant 'to give wages' or 'to employ'; over time 'regularly' came to mean 'on a recurring schedule' and combined with 'hired' it now denotes being 'employed on a regular or recurring basis.'