First-class on railway the Italian boards in a casual manner (6)
I believe the answer is:
airily
'in a casual manner' is the definition.
I can't judge whether this defines the answer.
'first-class on railway the italian boards' is the wordplay.
'first class' becomes 'ai' (A1 - top quality).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'railway' becomes 'ry' (abbreviation).
'the italian' becomes 'il' (Italian for 'the').
'boards' is an insertion indicator.
'ry' placed around 'il' is 'rily'.
'ai'+'rily'='AIRILY'
Can you help me to learn more?
(Other definitions for airily that I've seen before include "In a light manner" , "In a delicate manner" , "Breezily" , "In a nonchalant way" , "In a jaunty manner" .)