Calm suspicion, avoiding railway lines (5)
I believe the answer is:
quell
'calm' is the definition.
(thesaurus)
'suspicion avoiding railway lines' is the wordplay.
'suspicion' becomes 'query' (a query is a suspicion or question).
'avoiding' indicates named letters should be taken away.
'railway' becomes 'ry' (abbreviation).
'lines' becomes 'll' (l is an abbreviation for line).
'query' with 'ry' taken away is 'que'.
'que'+'ll'='QUELL'
(Other definitions for quell that I've seen before include "Extinguish" , "Put down" , "Suppress completely" , "Subdue, suppress" .)