A covering letter to G.B.S. (5)
I believe the answer is:
shawl
'a covering' is the definition.
(shawl is a kind of covering)
'letter to g b s' is the wordplay.
I cannot really see how this works, but
'letter' could be 'w' and 'w' is found in the answer.
's' is found in the answer.
The remaining letters 'hal' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for shawl that I've seen before include "Female garment" , "Stole or wrap" , "Cloth wrapped over one's shoulders" , "Baby wrapper" , "Garment for wrapping" .)