Girl's top, simply ghastly part of uniform (3,4)

I believe the answer is:

gym slip

'part of uniform' is the definition.
(part of a traditional girls' gym slip)

'girl's top simply ghastly' is the wordplay.
'top' says to take the initial letters.
'ghastly' indicates anagramming the letters (a ghastly spelling of the words).
The initial letter of 'girl' is 'g'.
'simply' with letters rearranged gives 'ymslip'.
'g'+'ymslip'='GYM SLIP'

I've seen this clue in The Guardian.

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