More friendly, more familiar, or more inclined to be chummy than something else.
From 'chummy' (friendly, familiar) plus the comparative suffix '-er.' 'Chummy' comes from 'chum,' with '-y' making it an adjective meaning 'like a chum' or 'acting as a chum.'
You can literally measure friendship in English grammar—'chummy' is a descriptor, 'chummier' means you're getting closer, and 'chummiest' means you're basically inseparable.
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