Cantankerous individual welcoming king to railway (6)
I believe the answer is:
ornery
'cantankerous' is the definition.
('ornery' can be a synonym of 'cantankerous')
'individual welcoming king to railway' is the wordplay.
'individual' becomes 'one'.
'welcoming' is an insertion indicator (in sense of 'inviting in').
'king' becomes 'r' (r is abbreviation for rex).
'to railway' becomes 'ry' (abbreviation for railway).
'one' enclosing 'r' is 'orne'.
'orne'+'ry'='ORNERY'
(Other definitions for ornery that I've seen before include "Mean - stubborn" , "Awkward" , "Cantankerous or mean (US)" , "Difficult to deal with" .)