Relating to or found in an estuary; marked by the mixture of salt water from the ocean and fresh water from rivers.
From 'estuary' plus '-ine' (adjective suffix). Became the standard scientific term by the 19th century for describing this specific coastal ecosystem type.
Estuarine is the term you'll find in every ecology textbook because scientists needed a precise word for this uniquely challenging environment where organisms must tolerate constantly changing salinity.
Complete word intelligence in one call. Free tier — 50 lookups/day.