They're adult in many ways (3)
I believe the answer is:
men
'ways' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe there's an association between them I don't understand?
'they're adult in many' is the wordplay.
I cannot quite understand how this works, but
'many' could be 'm' (Roman numeral for a thousand) and 'm' is located in the answer.
The remaining letters 'en' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for men that I've seen before include "Soldiers" , "'So many ..., so many opinions'" , "Fellows, chaps" , "Adult males" , "- - -o'-war (ships)" .)