Uninteresting commercial for nymph (5)
I believe the answer is:
dryad
'for nymph' is the definition.
(dryad is a kind of nymph)
'uninteresting commercial' is the wordplay.
'uninteresting' becomes 'dry' (dry can mean dull or boring).
'commercial' becomes 'ad' (abbreviation for advertisement).
'dry'+'ad'='DRYAD'
(Other definitions for dryad that I've seen before include "Wood-nymph" , "Tree nymph" , "Mythological wood nymph" , "one stuck in a tree" , "Beautiful young woman" .)