Plural of anti; people who oppose a particular person, policy, cause, or movement.
From anti-, the prefix or standalone word meaning 'against.' Used colloquially since the early 20th century, especially in American English.
The word 'antis' is interesting because it's vague—you could be antis about almost anything, making it a quick shorthand for people who define themselves mainly by what they're against rather than what they're for.
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