slow in comprehension; blockheaded;

 insensitive

to wither away;

to decline from disuse

astute

quick in discernment;

shrewd;

 clever or keen

to condemn;

to expose critically

to seek to reach a goal;

 to aim for something one hopes to achieve

an award;

an honor;

approval or praise

easily taught or controlled; obedient;

easy to handle

unsafe;

unsteady;

unstable