Drunk embraces copper — it may indicate warmth (7)
I believe the answer is:
mercury
'it may indicate warmth' is the definition.
(mercury in a thermometer)
'drunk embraces copper' is the wordplay.
'drunk' becomes 'merry' (merry can mean cheerfully drunk).
'embraces' is an insertion indicator.
'copper' becomes 'cu' (chemical symbol).
'merry' placed around 'cu' is 'MERCURY'.
(Other definitions for mercury that I've seen before include "Planet nearest the sun" , "Atomic number 80" , "one in distant orbit?" , "Element, symbol Hg" , "First planet from the Sun" .)