### Clue: Articulation that is ultimately quick on the uptake and keen to change (4)
### Answer: KNEE 
 ### Explanation: Definition: Articulation
 Double wordplay. 1st: **The last letters, respectively, of**(ultimately) "quick on the uptake"; and 2nd: **Anagram of**(… to change) KEEN.
Defn: An anatomical joint.