'trout-stream' originates from English, specifically the combination of the nouns 'trout' and 'stream', where 'trout' originally meant 'a freshwater fish of the family Salmonidae' and 'stream' meant 'a flowing body of water'.

'trout' developed from Old English forms (such as 'truht'/'trūt' and Middle English 'trout(e)') and 'stream' from Old English 'stream'/'stre(a)m'; the modern compound 'trout-stream' arose by combining these established nouns in Modern English.

Initially it referred straightforwardly to a stream where trout occur; over time the phrase has retained that basic meaning, used descriptively for streams known for trout.