Buttress with ends of segment touching, and no good, therefore (10)
I believe the answer is:
strengthen
'buttress' is the definition.
(thesaurus)
'ends of segment touching and no good therefore' is the wordplay.
'ends of segment' becomes 'st' (I am not sure about this - if you are sure you should believe this answer much more).
'touching' becomes 're' (re can mean touching or regarding).
'and' is a charade indicator (letters next to each other).
'no good' becomes 'ng' (abbreviation for no and good).
'therefore' becomes 'then' (I've seen this in another clue).
'st'+'re'+'ng'+'then'='STRENGTHEN'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for strengthen that I've seen before include "Brace" , "Toughen up" , "Make more powerful" , "rally" , "Build up" .)