Of or relating to an estuary; found in or characteristic of the area where a river meets the sea.
From 'estuary' plus '-ian' (adjective suffix), an alternate form of '-ial'. Both are valid, with '-ian' often preferred in some regions.
Estuarian and estuarine mean the same thing, but you'll notice 'estuarine' is far more common in modern English—language naturally favors the shorter, more efficient form.
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