A trap set thus is not together (5)
I believe the answer is:
apart
'is not together' is the definition.
(I've seen this in another clue)
'a trap set' is the wordplay.
'set' indicates anagramming the letters (instruction to set the letters).
'trap' is an anagram of 'part'.
'a'+'part'='APART'
'thus' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for apart that I've seen before include "Divided" , "in bits" , "First Christmas present from my love" , "Unconnected" , "Cut off - in pieces" .)