'antirealistically' originates from the prefix 'anti-' (from Greek ἀντί) meaning 'against' or 'opposite,' combined with 'realistic' (from 'real' + suffix '-istic'), ultimately tracing back to Latin 'realis' from 'res' meaning 'thing'.

'antirealistically' developed by attaching the English adjectival suffix '-istic' to 'real' (from Latin 'realis'), forming 'realistic,' then prefixed by 'anti-' to form 'antirealistic,' and finally adding the adverbial suffix '-ally' to create 'antirealistically.'

Initially composed elements meant 'against' + 'pertaining to the real' (i.e., opposing a realist stance); over time this combination came to be used specifically to describe speech or argumentation 'in a manner opposing realism,' which is the current usage.