What you use to tell the time.
clock
A group of sheep.
flock
A type of music.
rock
A place to park boats.
dock
A type of apron.
smock
A soft article of clothing that goes on the foot.
sock
A sound a clock might make.
tock
A cube that you build with.
block
What you should do to the door when you leave.
lock
To tap on the door.
knock