'trade-unionist' originates from English, specifically a compound of 'trade' + 'union' + the suffix '-ist' (denoting a person associated with a practice or ideology), where 'union' came from Latin 'unio' meaning 'oneness'.

'trade' (Old English related words) + 'union' (from Latin 'unio' via Old French 'union') combined in modern English to form 'trade union' in the 19th century; the agentive form 'trade-unionist' then developed to denote a person who supports or belongs to a trade union.

Initially coined to describe a supporter or member of a trade union, its meaning has remained largely the same: a person who advocates for or belongs to a workers' union.