Joint in the Spanish area of London (5)
I believe the answer is:
elbow
'joint' is the definition.
(joint of the body)
'the spanish area of london' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'area of london' becomes 'bow' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'el'+'bow'='ELBOW'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for elbow that I've seen before include "Jostle" , "Hinge joint" , "Sharp bend in a road or river" , "sack?" , "Sort of grease" .)