For which very long-term use results ultimately in wear and tear, say (6)
I believe the answer is:
rhymes
'wear and tear say' is the definition.
('wear' and 'tear' rhyme with each other)
I don't understand how the remainder of the clue works.
(Other definitions for rhymes that I've seen before include "Nursery . . . . . . are traditional verses for children" , "Nursery . . . . . . are simple ditties for children" , "Nursery . . . . . . are jingles for children" , "Pieces of verse" , "Similar sounds at the ends of lines of poetry" .)