Handyman's powder spotted above shower (7)
I believe the answer is:
sawdust
'handyman's powder' is the definition.
(sawdust might be created by a handyman's work)
'spotted above shower' is the wordplay.
'spotted' becomes 'saw' (I've seen this before).
'above' means one lot of letters go next to another.
'shower' becomes 'dust' (as in a shower of dust).
'saw'+'dust'='SAWDUST'
(Other definitions for sawdust that I've seen before include "Powdery wood particles" , "Wood chippings" , "fine wooden pieces" , "Powdery residue from cut wood" , "Carpenter's waste matter" .)