serious - definition and synonyms


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  1. 1
    bad or dangerous enough to make you worried

    The sale of the company will have serious implications for people’s jobs.

    a serious problem/mistake:

    It’s not a serious problem – we should be able to fix it without too much trouble.

    a serious illness/accident/injury:

    a serious head injury

    a serious crime/offence/threat:

    An accident like this poses a serious threat to the environment.

  2. 2
    important and deserving attention

    This is an extremely serious matter.

    He has no serious competition for the post.

     Synonyms and related words
  3. 3
    meaning what you say or do, and not making a joke

    I’m sorry, I didn’t realize you were being serious.

    The police have made no serious attempt to address these issues.

    serious about:

    I’m not convinced they’re serious about the deal.

    serious about (doing) something:

    Do you think Mike’s serious about going to live in New Zealand?

    deadly/dead (=completely) serious:

    ‘Are you serious about leaving your job?’ ‘Dead serious.’

  4. 4
    careful and detailed
    serious consideration/thought/discussion:

    We’ll have to give the situation some serious thought.

  5. 5
    someone who is serious thinks carefully about things and does not laugh much

    Peter seems serious but he actually has a good sense of humour.

    1. a.
      appearing worried or upset

      Is Mary all right? She looked a bit serious.

  6. 6
    [usually before noun] dealing with important, complicated, or difficult ideas or subjects

    serious books/music

  7. 7
    if you are in a serious romantic relationship with someone, you intend to stay together for a long time

    Is it getting serious with you and June, then?

    a serious boyfriend/girlfriend/relationship:

    He’s never had a serious relationship with anyone.

  8. 8
    involved in an activity in a way that shows you like it a lot and think it is important

    My father is a serious runner.

  9. 9
    informal extreme, or large in amount

    We did some serious hiking last weekend.

    It’s time you made some serious money.

derived word



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noun [uncountable]