Somewhat like a duck; having duck-like qualities, manners, or characteristics; resembling a duck.
From 'duck' plus the suffix '-ish' (meaning having qualities of something or somewhat resembling). This is a productive suffix in English creating adjectives like 'childish' and 'foolish.'
The suffix '-ish' is wonderfully vague—'duckish' could mean literally resembling a duck, acting cowardly like a duck, or even just having something indefinably duck-related about you.
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