Water as a chemical substance. / (Malaysia, Internet slang, humorous, politics) Hishammuddin Hussein Onn, Malaysian politician and son of Hussein Onn, third prime minister of Malaysia.

(mathematical analysis) Upper bound function; see big O notation. / (slang, usually preceded by "the") Orgasm.

(US, Canada) A brand of dessert made from gelatin. / (by extension) Any brand of fruit flavored gelatin dessert mix.

(computing, electrical engineering) input/output

The national anthem of Canada

(informal) standing ovation

(electronics, informal) oscilloscope

plural of o-scope

(Australia and New Zealand colloquial, now historical) Someone who sells rabbits for food, especially an itinerant salesman.

Informal form of of course.