Spoke of progress with gravity (4)
I believe the answer is:
rung
'spoke' is the definition.
(synonyms)
'of progress with gravity' is the wordplay.
'of progress' becomes 'run' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'with' means one lot of letters go next to another.
'gravity' becomes 'g'.
'run'+'g'='RUNG'
Can you help me to learn more?
(Other definitions for rung that I've seen before include "Horizontal bar in ladder" , "support for foot" , "spoke" , "Tolled - step on ladder" , "Step up the ladder - called for" .)