Top of a semicolon (3)
I believe the answer is:
dot
'top of a semicolon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dot that I've seen before include "Point; speck" , "Spot, speck" , "Very small circular shape" , "Tiny speck" , "One signal used in Morse code" .)