Gruesome lairs tons avoided (7)
I believe the answer is:
hideous
'gruesome' is the definition.
(thesaurus)
'lairs tons avoided' is the wordplay.
'lairs' becomes 'hideouts' (I've seen this before).
'tons' becomes 't'.
'avoided' indicates named letters should be taken away.
'hideouts' with 't' removed is 'HIDEOUS'.
(Other definitions for hideous that I've seen before include "Extremely ugly" , "Ghastly" , "Extremely unpleasant" , "Frightful" , "Repulsive" .)