Constant tease in bed (4)
I believe the answer is:
crib
'bed' is the definition.
(thesaurus)
'constant tease' is the wordplay.
'constant' becomes 'c' (mathematical abbreviation).
'tease' becomes 'rib' (I've seen this before**).
'c'+'rib'='CRIB'
'in' acts as a link.
(Other definitions for crib that I've seen before include "Copy someone else's work" , "Nativity model" , "Translation; bed" , "Pen" , "Card game for two" .)