Deserter hiding in oddly clear hollow (6)
I believe the answer is:
crater
'hollow' is the definition.
(thesaurus)
'deserter hiding in oddly clear' is the wordplay.
'deserter' becomes 'rat' (I've seen this before).
'hiding in' means one lot of letters goes inside another.
'oddly' means one should take alternating letters.
The alternating letters of 'clear' are 'cer'.
'rat' placed within 'cer' is 'CRATER'.
(Other definitions for crater that I've seen before include "Fissure in the earth's crust" , "Volcanic depresssion" , "Cavity formed by explosion" , "Hole left by explosion" , "Hole (on the moon?)" .)