Run racehorses together (6)
I believe the answer is:
string
'run racehorses' is the definition.
'string' can be an answer for 'racehorses' (I've seen this before). I'm unsure of the 'run' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for string that I've seen before include "Hard to say how long a piece of it is" , "tier" , "Part of racket" , "How long could a piece of it be?" , "Group of racers" .)