Firmly hold 150 snakes (6)
I believe the answer is:
clasps
'firmly hold 150 snakes' is the definition.
I can't tell whether this definition defines the answer.
'150 snakes' is the wordplay.
'150' becomes 'CL' (roman numerals).
'snakes' becomes 'asps' (asp is a kind of snake).
'cl'+'asps'='CLASPS'
Can you help me to learn more?
(Other definitions for clasps that I've seen before include "Fasteners, as on necklaces perhaps" , "Necklace fasteners" , "Embraces; fastenings" , "Holds the fastenings to one's bosom" , "Holds tightly" .)