Uncertain motion of a broken elbow about to start bending (6)
I believe the answer is:
wobble
'uncertain motion' is the definition.
'wobble' can be an answer for 'motion' (wobble is a kind of motion). I am not sure about the 'uncertain' bit.
'broken elbow about to start bending' is the wordplay.
'broken' indicates an anagram.
'about' indicates putting letters inside.
'to start' suggests taking the first letters.
The first letter of 'bending' is 'b'.
'elbow' is an anagram of 'woble'.
'woble' placed around 'b' is 'WOBBLE'.
'of a' is the link.
Can you help me to learn more?
(Other definitions for wobble that I've seen before include "Oscillate" , "Move unsteadily (like a jelly?)" , "Stand unsteadily, rock a little" , "Sway unsteadily" , "unstable motion" .)
