A part that can't be matched (7)
I believe the answer is:
oddment
'a part that can't be matched' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
This is the entire clue.
Can you help me to learn more?
(Other definitions for oddment that I've seen before include "Leftover piece" , "An isolated article, something left over" , "Piece left over, no match" , "Curiosity, peculiarity" , "spare part?" .)