Final defeat that's the end of the line? (8)
I believe the answer is:
waterloo
'final defeat' is the definition.
(I've seen this in another clue)
'the end of 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.
'of' could be 'o' and 'o' is found within the answer.
'line?' could be 'l' (used when specifying particular lines from a poem) and 'l' is located in the answer.
This explanation may well be incorrect...
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for waterloo that I've seen before include "Napoleonic end" , "Seminal European battle of 1815" , "Tracked site" , "where trains come and go" , "Definitive battle of the Napoleonic Wars" .)