Flask of rum or meths (7)
I believe the answer is:
thermos
'flask' is the definition.
(thermos is a kind of flask)
'rum or meths' is the wordplay.
'rum' indicates anagramming the letters (rum can mean strange or unusual).
'or'+'meths'='ormeths'
'ormeths' anagrammed gives 'THERMOS'.
'of' acts as a link.
(Other definitions for thermos that I've seen before include "Heat-retaining flask for mothers" , "Container to retain heat" , "Vacuum flask for mothers" , "Flask trade mark" .)