...one whose job is on the line (9,6)
I believe the answer is:
tightrope walker
'one' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?
'job is on the line' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'line' could be 'walk' (walk is a kind of line) and 'walk' is located in the answer.
This explanation may well be incorrect...
'whose' is the link.
Can you help me to learn more?
(Other definitions for tightrope walker that I've seen before include "Charles Blondin, perhaps" , "As one taking highly risky steps" , "Circus performer" , "Funambulist'" , "circus act" .)