Low temperature is debatable (4)
I believe the answer is:
moot
'debatable' is the definition.
('moot' can be a synonym of 'debatable')
'low temperature' is the wordplay.
'low' becomes 'moo' ('moo' can be a synonym of 'low').
'temperature' becomes 't' (abbreviation).
'moo'+'t'='MOOT'
'is' is the link.
(Other definitions for moot that I've seen before include "Open to argument or debate" , "Undecided as a debatable point may be" , "raise for discussion" , "Open to question" , "Such a point is arguable" .)