Headgear that guy allows to protect back of cranium (7)
I believe the answer is:
helmets
'headgear' is the definition.
Although both the answer and definition are nouns, they are not in the same form of the noun.
'that guy allows to protect back of cranium' is the wordplay.
'that guy' becomes 'he'.
'allows to' becomes 'lets' (I've seen this in another clue).
'protect' means one lot of letters goes inside another.
'back of' says to take the final letters.
The final letter of 'cranium' is 'm'.
'lets' placed around 'm' is 'lmets'.
'he'+'lmets'='HELMETS'
Can you help me to learn more?
(Other definitions for helmets that I've seen before include "Protective head plates" , "Protective head coverings" , "Protective head-gear" .)