Jockey let teeth rot: exactly! (2,3,6)
I believe the answer is:
to the letter
'exactly' is the definition.
(I've seen this before)
'jockey let teeth rot' is the wordplay.
'jockey' is an anagram indicator (the letters scramble or jockey around).
'let'+'teeth'+'rot'='letteethrot'
'letteethrot' anagrammed gives 'TO THE LETTER'.
(Other definitions for to the letter that I've seen before include "Adhering to strict detail" , "From the tenant, presumably" , "giving every detail" , "Exactly" , "Following every detail" .)