Publicise irregular spot (6)
I believe the answer is:
splash
'spot' is the definition.
(both can mean a splodge or blot)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for splash that I've seen before include "Effect of fall into water" , "Dash with liquid" , "Bright patch of colour; fall in drops" , "Cause liquid to fly about in drops" , "Big newspaper feature" .)