For your trip from A to B, the A -> B leg might be referred to as
outbound ( leg / trip )
going
outward (journey)
The B -> A (return) leg might be referred to as
inbound
coming
return (leg / trip)
home leg (if A is your home)
homeward
An "onward" journey implies you are at a transfer point and there is further travelling until you reach your final destination.
In AmE the A -> B -> A trip is referred to as a "roundtrip", in BrE it is simply referred to as a "return"
"Two roundtrip tickets to Boston, please."
"Two return tickets to Nottingham, please."
As a related but side note:
POSH = port "out", starboard "home"
the more comfortable side of the ship between England and India