Went fast - yet at disheartening speed? (4)
I believe the answer is:
sped
'went fast' is the definition.
(I've seen this in another clue)
'disheartening speed?' is the wordplay.
'disheartening' means to remove the middle letters.
'speed' with its middle removed is 'SPED'.
'yet at' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sped that I've seen before include "got a move on" , "Raced, hurried" , "Went fast" , "Made haste" , "Moved fast" .)