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on

prep. · adv. · adj.
  1. 1 location or surface (prep.)
    A1 Beginner

    touching the top or side of a surface.

    indicating a position in physical contact with and supported by a surface.

    Example

    He left his phone on the kitchen table while he went to get his keys.

    Example

    The delicate porcelain vase sat precariously on the edge of the mantelpiece, vibrating slightly every time a heavy truck passed the house.
    Pitfall
    The book is in the table.
    The book is on the table.

    Use 'on' for surfaces; 'in' is for things inside a container or 3D space.

  2. 2 days and dates (prep.)
    A1 Beginner

    used to show the day or date when something happens.

    indicating a specific day or calendar date.

    Example

    The party is on Saturday evening, so I hope you can come.

    Example

    The treaty was officially signed on the twelfth of October, marking the end of nearly a decade of border disputes.

    Usage

    Always used before specific days of the week or calendar dates.

    Pitfall
    I will see you in Monday.
    I will see you on Monday.

    Use 'on' for specific days and dates; use 'in' for months, years, or seasons.

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  1. 3 about a subject (prep.)
    B1 Intermediate

    about or concerning a specific topic.

    concerning or dealing with a particular subject or area of study.

    Example

    She is writing a report on the history of the local park.

    Example

    The professor published a definitive monograph on the migration patterns of Arctic terns, drawing from twenty years of field data.

    Teacher's tip

    'On' is often used for more formal or academic topics compared to 'about'.
  2. 4 using a device (prep.)
    A2 Elementary

    using a machine, tool, or system like a phone or computer.

    indicating the medium or instrument used to perform an action or transmit information.

    Example

    I spent all morning on the computer trying to finish my homework.

    Example

    The news was first broadcast on the radio before being picked up by major television networks an hour later.
  3. 5 working or active (adv.)
    A1 Beginner

    in a state where a machine or light is working or providing power.

    indicating a state of being functional, operating, or switched to an active mode.

    Example

    Is the heating on? It feels very cold in here.

    Example

    The emergency lights came on automatically as soon as the main power grid failed during the storm.

    Usage

    Often follows the verb 'to be' or functions as a particle in phrasal verbs like 'turn on'.
  4. 6 continuing (adv.)
    B1 Intermediate

    continuing an action without stopping.

    indicating the continuation or progression of an action.

    Example

    They walked on for another mile despite the heavy rain.

    Example

    The speaker droned on for nearly two hours, oblivious to the fact that half the audience had already left the hall.

    Usage

    Commonly used with verbs of motion or duration like 'walk on' or 'go on'.
  5. 7 happening as planned (adj.)
    B1 Intermediate

    happening or taking place as scheduled.

    occurring or taking place; often used to describe events or performances.

    Example

    The festival is still on, even though it might rain later today.

    Example

    Despite the sudden resignation of the lead actor, the director insisted that the opening night performance was still on.

    Usage

    Usually functions as a predicative adjective after the verb 'to be'.
  6. 8 acceptable (adj.)
    B2 Upper Intermediate British English Informal

    fair or acceptable to do.

    appropriate, acceptable, or fair in a social or competitive context.

    Example

    Asking me to work through my lunch break is just not on.

    Example

    The committee decided that such a blatant conflict of interest was simply not on, and they demanded a full investigation.

    Teacher's tip

    Commonly used in the negative ('it's just not on') to describe unfair behaviour.
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