American boarding train for famous race meeting (5,5)
I believe the answer is:
royal ascot
'race meeting' is the definition.
(I've seen this before)
'american boarding train' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'boarding' is an insertion indicator.
'train' becomes 'royal scot' (former British train).
'a' put inside 'royalscot' is 'ROYAL ASCOT'.
'for famous' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for royal ascot that I've seen is " race meeting".)