Writer of verses for Mass (5)
I believe the answer is:
pound
'for mass' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for pound that I've seen before include "Pummel" , "Sixteen ounces" , "Weight - currency - beat - enclosure" , "British currency" , "100 6 [PENNIES]" .)