Spice humour displays such a low rental (10)
I believe the answer is:
peppercorn
'spice' is the definition.
(thesaurus)
'humour displays such a low rental' is the wordplay.
I cannot really see how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for peppercorn that I've seen before include "providing little income for landlord" , "Nominal" , "source of condiment" , "See this ground by mill" , ">something spicy" .)