Protection for head which has squeezed in (3,3)
I believe the answer is:
tin hat
'protection for head which has squeezed in' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'protection for head which' is the wordplay.
'protection for' means one lot of letters goes inside another (some letters go around or protect others).
'head' becomes 'in' (I can't justify this - if you can you should believe this answer much more).
'which' becomes 'that'.
'in' put into 'that' is 'TIN HAT'.
Can you help me to learn more?
(Other definitions for tin hat that I've seen before include "Soldier's helmet" , "Headgear, worn for protection" , "Steel helmet (informal)" , "Protective helmet once worn by constuction and mine workers" , "Finish it off to put the protective headgear on it" .)