Annexes, or small rooms, clubs let out (4)

I believe the answer is:
ells
'annexes' is the definition.
(I know this)
'small rooms clubs let out' is the wordplay.
I cannot quite understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is found in the answer.
The remaining letters 'ell' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'or' acts as a link.
Can you help me to learn more?
(Other definitions for ells that I've seen before include "Extensions to buildings at right angles: archaic cloth measurements" , "Old yards" , "Cloth measures" , "Lengths of cloth" , "Old English lengths" .)
