Allowed to perform in just a vest (7)
I believe the answer is:
singlet
'a vest' is the definition.
(I know that vest can be written as singlet)
'allowed to perform in' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'to' says to put letters next to each other (I've seen this in other clues).
'perform in' becomes 'sing' (to perform a song. I am not sure about the 'in' bit.).
'let' put after 'sing' is 'SINGLET'.
'just' acts as a link.
Can you help me to learn more?
(Other definitions for singlet that I've seen before include "garment worn by men" , "Sleeveless garment" , "Sleeveless shirt" , "Sleeveless vest" , "top gear" .)