Oddly their maths symbol is at end of line (8)
I believe the answer is:
terminus
'line' is the definition.
(thesaurus)
'oddly their maths symbol is at end of' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'maths symbol' becomes 'minus' (take away sign).
'is at end of' says to put letters next to each other (some letters go at the end of others).
The alternate letters of 'their' are 'ter'.
'ter'+'minus'='TERMINUS'
(Other definitions for terminus that I've seen before include "boundary marker" , "Limit" , "journey's end" , "eg Paddington" , "End of the line for tram or bus" .)