'avocational' originates from Latin, specifically from the verb 'avocare' (past participle/noun form 'avocatio'), where 'ab-' (rendered as 'a-') meant 'away' and 'vocare' meant 'to call'.

'avocare' (Latin) passed into Medieval/Old French and Middle English as 'avocation' (Old French/Medieval Latin forms), later forming the adjective 'avocational' and then the adverb 'avocationally' in modern English.

Initially it meant 'a calling away' or 'the act of calling aside'; over time it evolved to mean 'a diversion from one's main occupation' (i.e. a hobby or secondary pursuit), which is the sense used in 'avocationally'.