'aginner' originates from American English, specifically a colloquial formation from 'agin' meaning 'against' and the suffix '-er' indicating a person.

'agin' was a dialectal variant of 'against' in some regions of the United States, and 'aginner' was formed to describe someone who is habitually against things.

Initially, it meant 'someone who is against something,' and this meaning has largely remained the same in modern usage.