Louche airmen abandoned swimmer (4)
I believe the answer is:
fish
'swimmer' is the definition.
(fish swim)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fish that I've seen before include "Ruff" , "Trawler's catch" , "Aquatic vertebrate" , "Search" , "Aquatic creature(s)" .)