Fungus damaged a cigar (6)
I believe the answer is:
agaric
'fungus' is the definition.
(agaric is a kind of fungus)
'damaged a cigar' is the wordplay.
'damaged' indicates anagramming the letters.
'a'+'cigar'='acigar'
'acigar' is an anagram of 'AGARIC'.
(Other definitions for agaric that I've seen before include "fungal growth" , "Fungus of mushroom family" , "Fungus, eg, mushroom" , "Type of mushroom" .)