Glass could make men cool (7)
I believe the answer is:
monocle
'glass' is the definition.
(I've seen this before)
'make men cool' is the wordplay.
'make' indicates an anagram.
'men'+'cool'='mencool'
'mencool' anagrammed gives 'MONOCLE'.
'could' acts as a link.
(Other definitions for monocle that I've seen before include "Single eyeglass" , "Reading glass for one eye only" , "optical device" , "One-lens seeing apparatus" , "lens" .)