Busy tenant (6)
I believe the answer is:
occupy
I believe this is a double definition.
'busy' is the first definition.
(I know that busy can be written as occupy)
'tenant' is the second definition.
(thesaurus)
(Other definitions for occupy that I've seen before include "Hold (a position) keep (someone) busy" , "Interest" , "Engage the attention of" , "Inhabit, take up space" , "Fill up; hold (a position)" .)