High speed means heavy weight (3)
I believe the answer is:
ton
This clue could be a double definition.
'high speed' is the first definition.
'ton' can be an answer for 'speed' (I've seen this before). I'm not sure about the 'high' bit.
'heavy weight' is the second definition.
(a ton weighs a lot)
'means' acts as a link.
Can you help me to learn more?
(Other definitions for ton that I've seen before include "2,240 lbs" , "Two thousand, two hundred and forty lb" , "A slangy 100mph - heavy going" , "Style" , "Twenty cwt" .)