on one meaning

[British slang]
Phrs. Acting in a slightly crazed way. E.g."I'm going home. Andy's on one and he's annoying me.”

• -one:     /-ōn/ (chem)  ...
• a one for:     (informal) & ...
• a-one:    Adjective: A-oneOf ...

Examples

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1. she had given it expressly on one side.
2. he stretched out on one of its broad limbs.
3. the kind advice rests easily on one 's conscience.
4. a gruff voice jars on one 's nerves.
5. on one point she was resolved.