A small fish, possibly a young or female fish, or a fish that feeds in shallow waters like a hen might.
Compound of 'hen' (female bird, or used to diminish or feminize) and 'fish,' likely a folk or colloquial term from Northern European fishing traditions.
Folk names for fish often reveal what common people observed—if henfish referred to small fish found where hens waded, it's a perfect example of how nature observation created our oldest vocabulary!
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