Keeping time with part of the foot (6)
I believe the answer is:
instep
'the foot' is the definition.
(thesaurus)
'keeping time with part' is the wordplay.
'keeping time' becomes 'step' (I am not sure about this - if you are sure you should believe this answer much more).
'with' means one lot of letters go next to another.
'part' becomes 'in part' (synonyms).
'step' put after 'in' is 'INSTEP'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for instep that I've seen before include "downtrodden area" , "Top of foot" , "Upper surface of the foot" , "Foot arch - conforming" , "Part of foot under spinet" .)