Firm it should go on the second list (6)
I believe the answer is:
stable
'firm' is the definition.
(similar in meaning)
'on the second list' is the wordplay.
'on' says to put letters next to each other.
'the second' becomes 's' (common abbreviation).
'list' becomes 'table' (I've seen this before).
's' next to 'table' is 'STABLE'.
'it should go' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for stable that I've seen before include "Steady, unchanging" , "Place of birth" , "Steady, enduring" , "Where horses are kept" , "Steady in the outhouse" .)