It facilitates the movement of arms (5)
I believe the answer is:
elbow
'it facilitates' is the definition.
The definition suggests a singular noun which matches the answer.
'movement of arms' is the wordplay.
'movement of' becomes 'el' (I can't explain this - if you can you should give a lot more credence to this answer).
'arms' becomes 'bow' (bow is a kind of arms).
'el'+'bow'='ELBOW'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for elbow that I've seen before include "Below (anag.)" , "sharp turn" , "Barge" , "Sharp bend in a road or river" , "Sort of grease" .)