His hobby has a set purpose (9)
I believe the answer is:
collector
This could be a double definition.
'his hobby has a' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'set purpose' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for collector that I've seen before include "Accunulator, gatherer" , "One who accumulates things" , "Accumulator, gatherer" , "Acquirer of antiques, taxes, etc" , "One who likes to amass things" .)