James reported error in part of school uniform (7)

I believe the answer is:
gymslip
'part of school uniform' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'james reported error' is the wordplay.
'james' becomes 'jim' (short for James).
'reported' shows a homophone (sound like).
'error' becomes 'slip' (slip is a kind of error).
'jim' is a homophone of 'gym'.
'gym'+'slip'='GYMSLIP'
'in' is the link.
Can you help me to learn more?
(Other definitions for gymslip that I've seen before include "Girl's short sports dress" , "Schoolgirl's PE uniform" , "Tunic worn by schoolgirls" , "Former schoolgirl's wear" , "schoolgirl attire" .)
