One who gushes; a person who expresses emotions or words in an excessively enthusiastic or effusive manner.
From gush (to flow out rapidly) plus agent suffix '-er' (one who does), creating a descriptor for someone prone to gushing behavior.
The suffix '-er' is English's most productive word-building tool—by adding it to any verb, you instantly create someone who does that action, which is why you can invent words like 'googler' and everyone understands them.
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