Finishes OK, going first-class to the terminus (4,4)

'finishes ok going' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'first-class to the terminus' is the wordplay.
I cannot quite see how this works, but
'class' could be 'swell' (I have seen 'First class' mean 'swell' so perhaps 'class' could also mean 'swell') and 'swell' is found within the answer.
'terminus' could be 'end' (eg the end of a train line is its terminus) and 'end' is located in the answer.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?