Make slow progress as a tenor (5)
I believe the answer is:
drift
'tenor' is the definition.
(drift is a kind of tenor)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for drift that I've seen before include "Large heap (of snow)" , "state of indecision" , "Implication of what's been said" , "Wander aimlessly" , "Bank (of snow)" .)