One stuck in a green hole? (3)
I believe the answer is:
pin
'hole?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'one stuck in a green' is the wordplay.
'one' becomes 'i' (Roman numeral).
'stuck in' indicates putting letters inside.
'a green' becomes 'pn' (I can't justify this - if you can you should believe this answer much more).
'i' placed inside 'pn' is 'PIN'.
Can you help me to learn more?
(Other definitions for pin that I've seen before include "Stick with flag placed in golf hole" , "Small object to fasten or attach" , "Fasten; a security code" , "form of identification" , "Skittle; chess attack" .)