Short of energy, they are terribly coarse (6)
I believe the answer is:
earthy
'coarse' is the definition.
(synonyms)
'short of energy they are terribly' is the wordplay.
'short of' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'terribly' indicates an anagram.
'they'+'are'='theyare'
'theyare' with 'e' taken away is 'thyare'.
'thyare' anagrammed gives 'EARTHY'.
(Other definitions for earthy that I've seen before include "Resembling soil" , "Coarse like clay" , "Like soil; uninhibitedly direct" , "Hearty and lusty" , "Crude - vulgar" .)