Ad or Add
an ad is an advertisement (informal)
add- put a thing on the other thing, increase
- What a germ this ad / add you have put in the magazine.
- If you ad / add in some lemon juice the taste will be better.
- Spaghetti is aded / added when water has boiled and been salted.
- No ad / add is allowed while making a speech at the conference.
- That ad / add campaign was an absolute masterstroke.