Beat most of the nick (5)
I believe the answer is:
throb
'beat' is the definition.
(I know that throb is a type of beat)
'most of the nick' is the wordplay.
'most of' means to remove the last letter.
'nick' becomes 'rob' (both can mean to steal).
'the' with its last letter removed is 'th'.
'th'+'rob'='THROB'
(Other definitions for throb that I've seen before include "Palpitate, quiver (with emotion)" , "Strong rhythmic beat" , "beat repeatedly" , "One's heart may do it" , "Drum" .)