The notion that steak is only about a pound (6)
I believe the answer is:
belief
'the notion' is the definition.
(synonyms)
'steak is only about a pound' is the wordplay.
I cannot quite see how this works, but
'is' could be 'be' and 'be' is present in the answer.
'pound' could be 'l' (the pound sign is based on an L) and 'l' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'that' is the link.
Can you help me to learn more?
(Other definitions for belief that I've seen before include "Faith, credence" , "Credo" , "Faith, doctrine" , "Persuasion" , "Trust, faith (6)" .)