Infested with maggots or fly eggs; spoiled or tainted; also meaning disreputable or shabby.
From 'flyblow' (past participle 'blown'). Originally literal—meat infested with fly larvae—later used metaphorically for anything corrupted or degraded.
Calling something 'flyblown' was the perfect insult—it literally meant it was crawling with parasites, so the word became shorthand for anything rotten, corrupt, or worthless.
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