Retreats as a spider moves around quietly (10)
I believe the answer is:
disappears
'retreats' is the definition.
(to retreat is to disappear or leave)
'as a spider moves around quietly' is the wordplay.
'moves' indicates an anagram.
'around' indicates putting letters inside.
'quietly' becomes 'p' (p for piano and quiet).
'as'+'a'+'spider'='asaspider'
'asaspider' is an anagram of 'disapears'.
'disapears' going around 'p' is 'DISAPPEARS'.
(Other definitions for disappears that I've seen before include "becomes lost" , "goes missing" .)