Relating to large masses may be called wisdom (5)
I believe the answer is:
molar
This clue is a double definition.
'relating to large masses' is the first definition.
(molar can mean relating to mass)
'may be called wisdom' is the second definition.
(as in wisdom teeth)
(Other definitions for molar that I've seen before include "Grinding tooth in the back of a mammal's mouth" , "Type of tooth" , "Large tooth" , "part of the daily grind" , "Dealing with masses" .)