Clothing, one at a time (7)
I believe the answer is:
singlet
'clothing' is the definition.
(singlet is a kind of clothing)
'one at a time' is the wordplay.
'one' becomes 'single' ('single' can be a synonym of 'one').
'at a time' becomes 't' (I can't justify this - if you can you should believe this answer much more).
'single'+'t'='SINGLET'
Can you help me to learn more?
(Other definitions for singlet that I've seen before include "Sleeveless shirt" , "Sleeveless vest" , "underclothing" , "Underwear" , "garment worn by men" .)