on
Used to indicate position above and in contact with a surface, or attachment to something.
Definitions
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1
Positioned on top of or in contact with a surface.
“The cat is sitting on the warm wooden table.”
The cat is sitting on the warm wooden table.
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2
Occurring on a specific day or date.
“The big school meeting is on Friday morning.”
The big school meeting is on Friday morning.
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3
Operating or active (of a device, machine, or system).
“Please make sure the lights are on before you leave.”
Please make sure the lights are on before you leave.
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4
Concerning or about a particular topic.
“She gave a long speech on the importance of clean water.”
She gave a long speech on the importance of clean water.
"On" is one of the most common words in English and functions not only as a preposition but also as an adverb (e.g., "keep on going") and as part of many phrasal verbs (e.g., "turn on," "hold on," "carry on"). Its exact meaning depends heavily on context.