Malodorous pigpen hosts tattoo (6)
I believe the answer is:
stinky
'malodorous' is the definition.
(I know that malodorous can be written as stinky)
'pigpen hosts tattoo' is the wordplay.
'pigpen' becomes 'sty' (synonyms).
'hosts' indicates putting letters inside (inserted letters are welcomed or hosted).
'tattoo' becomes 'ink' (ink can informally mean a tattoo).
'sty' placed around 'ink' is 'STINKY'.
(Other definitions for stinky that I've seen before include "Having an unpleasant smell" , "Humming" , "high" , "Foul-smelling" , "Odoriferous" .)