threadbare = thread + bare;we know jeans are made of thread,imagine and old jeans, so we can say that thread can be seen in bare eyes.
threas+bare....you wear clothes when barly your clothes look like clothes..till each thread come out......
THREADBARE - Something which has been READ BAAR BAAR...so it is common..or a cliche, banal stuff!!
Observe that 'threadbar' as 'read' + 'bar' [In hindi, it is bar, bar i.e repetitive]. So when you read same thing repetitively, you get 'over familiar' and it becomes 'common/trite' for you.
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