Serious man’s given a hearing (7)
I believe the answer is:
earnest
'serious' is the definition.
(similar in meaning)
'man's given a hearing' is the wordplay.
'man' becomes 'nest' (I can't justify this - if you can you should give a lot more credence to this answer).
'given' means one lot of letters go next to another.
'a hearing' becomes 'ear' (ear is a kind of hearing).
'nest' after 'ear' is 'EARNEST'.
Can you help me to learn more?
(Other definitions for earnest that I've seen before include "Oscar Wilde wrote ''The importance of Being . . . . . . . '' (7)" , "Oscar Wilde play 'The Importance of Being . . . . . . .'" , "showing seriousness" , "Eager, sincere" , "'Serious, sincere (7)'" .)