Like a Jenga tower just before toppling, often (5)
I believe the answer is:
shaky
(Other definitions for shaky that I've seen before include "Trembling; not safe" , "Not reliable; trembling" , "Not firm" , "Wobbly" , "Unstable; trembling" .)
I believe the answer is:
shaky
(Other definitions for shaky that I've seen before include "Trembling; not safe" , "Not reliable; trembling" , "Not firm" , "Wobbly" , "Unstable; trembling" .)