Owns toboggan, endless bother (6)
I believe the answer is:
hassle
'bother' is the definition.
(synonyms)
'owns toboggan endless' is the wordplay.
'owns' becomes 'has' ('have' can be a synonym of 'own').
'toboggan' becomes 'sled' (I've seen this before).
'endless' means to remove the last letter.
'sled' with its final letter removed is 'sle'.
'has'+'sle'='HASSLE'
(Other definitions for hassle that I've seen before include "Annoy continually" , "Harass - bother" , "Modern word for bother and annoyance" , "Colloquial harassment or annoyance" , "Informally annoy or bother" .)