Unit of heat energy (7)
(Other definitions for calorie that I've seen before include "Unit of heat energy" , "Unit of heat (concerned with diet)" , "Unit of energy in foods" , "generating a bit of heat" , "Food energy unit" .)
'unit of heat energy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for therm that I've seen before include "Former gas supply unit" , "Unit of heat used in the UK as the basis of gas bills" , "Indicator of heat" , "Unit of measurement of heat" , "Unit of heat as in gas supply" .)