A number possibly listen to the pulse (7)
I believe the answer is:
lentils
'the pulse' is the definition.
(I've seen this before)
'a number possibly listen' is the wordplay.
'a number' becomes 'l' (fifty in Roman numerals).
'possibly' indicates anagramming the letters.
'listen' is an anagram of 'entils'.
'l'+'entils'='LENTILS'
'to' acts as a link.
(Other definitions for lentils that I've seen before include "Protein-rich pulses" , "Pulse" , "Leguminous seeds for soup or stew" .)