Second half of larger tooth (5)
I believe the answer is:
molar
'tooth' is the definition.
(molar is a kind of tooth)
'second half of larger' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'half of' means to take half the letters.
'larger' with half the letters taken is 'lar'.
'mo'+'lar'='MOLAR'
(Other definitions for molar that I've seen before include "part of the daily grind" , "Type of tooth" , "Moral (anag.)" , "Grinding tooth in the back of a mammal's mouth" , "Large tooth" .)