'antitruster' originates from English, specifically the word 'antitrust', where 'anti-' meant 'against' and 'trust' meant 'a business organization or monopoly', and the agentive suffix '-er' meant 'person associated with or performing an action'.

'antitruster' changed from the modern English formation of 'antitrust' + the agent suffix '-er'; 'antitrust' itself developed in the late 19th century from 'anti-' + 'trust' (the business 'trust' meaning a large business combination), and adding '-er' produced 'antitruster' to denote a person holding antitrust views.

Initially it has meant 'a person opposing trusts or supporting antitrust policy', and this basic meaning has remained stable in modern usage.