In a feminine manner; in a way that displays qualities traditionally associated with women.
From 'feminine' plus the adverbial suffix '-ly,' which turns adjectives into adverbs. This allows speakers to describe how something is done in a feminine way.
Adding '-ly' to adjectives to make adverbs is one of the most productive word patterns in English, so you can make an adverb from almost any adjective—which is why 'femininely' feels natural even if you've never heard it before.
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