Being short, they're in urgent supply (5)

I believe the answer is:
gents
'being short' is the definition.
The definition and answer are not the same part of speech.
'in urgent supply' is the wordplay.
'in' indicates a hidden word.
'GENTS' can be found hidden inside 'urgent supply'.
'they're' is the link.
Can you help me to learn more?
(Other definitions for gents that I've seen before include "Public convenience" , "Men (colloq.)" , "toilet" , "Male loos" .)
