The word 'vicissitudinous' traces its lineage to the Latin noun 'vicis', meaning a turn, change, or alternation. This root evolved into 'vicissitudo', signifying a change of fortune, which was borrowed into English as 'vicissitude'. The adjective form was created by adding the English adjectival suffix '-ous' (meaning 'full of') to an adapted stem 'vicissitudin-', incorporating a connective '-in-' from the Latin source. Thus, the literal construction "full of changes of fortune" directly conveys the modern meaning of being subject to unpredictable shifts in life's conditions.

Structure: vicissitud (change) + in (adjective-forming suffix) + ous (adjective-forming suffix) - vicissitud: From Latin 'vicissitudo' (change, alternation), itself from 'vicis' (turn, change, alternation). - in: A Latin suffix often used to form nouns, which in this word serves as a connecting element. - ous: An English suffix from Latin '-osus', meaning 'full of' or 'characterized by'.