Terminal losing one-third of trains is not right for board? (9)
I believe the answer is:
uneatable
'terminal losing one-third of trains' is the definition.
I can't tell whether this definition defines the answer.
'not right for board?' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'right for board?' becomes 'eatable' (I am not sure about this - if you are sure you should believe this answer much more).
'un'+'eatable'='UNEATABLE'
'is' is the link.
Can you help me to learn more?
(Other definitions for uneatable that I've seen before include "disgusting when dining" , "can't be taken in!" , "not fit for consumption" , "Can't be kept down" , "pursued unspeakably?" .)