Teach fishes swimming (6)
I believe the answer is:
school
This clue might be a double definition.
'teach' is the first definition.
(thesaurus)
'fishes swimming' is the second definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
Can you help me to learn more?
(Other definitions for school that I've seen before include "Educational institution" , "For the education of fish" , "Group of pupils, fish" , "Teach; group of fish" , "Group of porpoises - place of education" .)