High temperature, and hard to swallow? (4)
I believe the answer is:
heat
'high temperature' is the definition.
(synonyms)
'hard to swallow?' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to swallow?' becomes 'eat' (I've seen this in another clue).
'h'+'eat'='HEAT'
'and' acts as a link.
(Other definitions for heat that I've seen before include "Vehemence" , "Warmth - gossip mag" , "Energy that caues a rise in temperature" , "Warmth - passion" , "Level of spice" .)