Passageway contains a form of meat (5)
I believe the answer is:
halal
'form of meat' is the definition.
The definition suggests a singular noun which matches the answer.
'passageway contains a' is the wordplay.
'passageway' becomes 'hall' (hall is a kind of passageway**).
'contains' is an insertion indicator.
'hall' enclosing 'a' is 'HALAL'.
Can you help me to learn more?
(Other definitions for halal that I've seen before include "which food is legal in Mecca" , "(Of meat) suitable for Muslims" , "special sort of meat" , "(Meat) from animals slaughtered according to Muslim law" , "Meat prepared for Muslims" .)