'antimerger' is a Modern English compound formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against') and 'merger,' derived from the verb 'merge' (from Latin 'mergere' meaning 'to plunge or immerse').

'merge' comes from Latin 'mergere' (through Medieval/Old French influences) and entered English with the sense of combining or joining; the compound 'antimerger' was created in Modern English by adding the productive prefix 'anti-' to 'merger'.

Originally 'mergere' meant 'to plunge or immerse'; in later usage 'merge' came to mean 'to combine or unite', and 'antimerger' thus came to mean 'against combining (of companies)'.