Did you know?

Click any word in a definition or example to find the entry for that word

thin - definition and synonyms


What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.



Thesaurus diagram

The thesaurus of synonyms and related words is fully integrated into the dictionary. Click on the thesaurus category heading under the button in an entry to see the synonyms and related words for that meaning.

verb     thin pronunciation in American English
Word Forms
present tense
present participlethinning
past tensethinned
past participlethinned
  • Facebook
  • Twitter
  1. 1



    thin down

    [transitive] to make something smaller in number, amount, or size

    Sales have decreased and we’ve decided to thin our workforce.

    Police thinned down the crowd.

    1. a.
      [intransitive] to become smaller in number, amount, or size
  2. 2



    thin out

    [transitive] to remove plants, leaves, trees, etc. so that they do not fill an area or space completely
    Synonyms and related words
  3. 3
    [transitive] to make a thick liquid become less thick by adding water or another liquid to it
  4. 4
    [intransitive] if someone’s hair thins, they gradually lose the hair from their head

    a man with gray thinning hair

Open Dictionary


a rise in the level of a stream or river

add a word


A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog
Macmillan learn live love play