Foundation to flex, repelling new swaying motion (7)
I believe the answer is:
bedrock
'foundation' is the definition.
(I have seen 'Solid foundation' mean 'bedrock' so perhaps 'foundation' could also mean 'bedrock')
'flex repelling new swaying motion' is the wordplay.
'flex' becomes 'bend' (synonyms).
'repelling' indicates named letters should be taken away.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'swaying motion' becomes 'rock' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bend' with 'n' taken out is 'bed'.
'bed'+'rock'='BEDROCK'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for bedrock that I've seen before include "Fundamental principle" , "Fundamental principles" , "Basis" , "Solid foundation" .)