Dull commercials showing nymphs (6)
I believe the answer is:
dryads
'nymphs' is the definition.
(dryads are tree nymphs in Greek myth)
'dull commercials' is the wordplay.
'dull' becomes 'dry' (I've seen this in another clue).
'commercials' becomes 'ads' (advertisements).
'dry'+'ads'='DRYADS'
'showing' is the link.
(Other definitions for dryads that I've seen before include "Nymphs of the woods" , "Tree-nymphs." , "spirits" , "Wood nymphs of legend" , "Tree nymphs" .)