underweight

underweight — adjective

1. Having a body weight that is lower than what is considered healthy or normal for

1.adjectiveB1
Definition

Having a body weight that is lower than what is considered healthy or normal for a person or animal of a certain height and age.

Example

The doctor told Lien that her kitten was slightly underweight and needed more food.

collocation: slightly underweight (degree modifier)

Many stray animals that arrive at the shelter are underweight and require special care.

Common collocations
  • slightly underweight
  • severely underweight
  • dangerously underweight
Synonyms
  • thin

    neutral term; does not necessarily imply a health concern

  • skinny

    informal, often carries a negative or critical tone

  • undernourished

    focuses on insufficient food intake rather than weight alone

  • emaciated

    much more extreme; describes someone dangerously thin from starvation or illness

Antonyms
  • overweight

    the opposite end of the weight spectrum

  • obese

    a more severe form of excess weight

Grammar Patterns

be + underweight

underweight + noun

Usage Note

Common in medical and health contexts. Frequently used with degree modifiers such as 'slightly,' 'severely,' or 'dangerously.'

Common Mistakes

The patient is underweight of 50 kilograms.
The patient is underweight at 50 kilograms.
Use 'at' not 'of' when stating a specific body weight.

underweight — noun

Word family

Synonym discussion

Sense: adjective/1

All four words describe a lack of body weight or fat, but they differ in severity and connotation. 'Thin' is the most neutral and general term — a person can be thin and perfectly healthy. 'Skinny' is informal and often carries a negative or critical tone, suggesting the person is too thin in the observer's opinion. 'Underweight' (the headword) is the clinical, objective term used by doctors and health professionals to indicate weight below a healthy threshold. 'Undernourished' shifts focus from weight to nutrition — someone can be undernourished without being severely underweight if they lack essential nutrients. 'Emaciated' is the most extreme term, describing someone who is dangerously thin, often from starvation, illness, or severe deprivation. For example, a doctor might note that a patient is 'underweight' and recommend a diet plan, while a news report about a famine might describe people as 'emaciated.'

thin ↗skinny ↗undernourished ↗emaciated

Common collocations

Nouns

Adverbs

Phrases

  • classified as underweight
  • diagnosed as underweight
  • at risk of being underweight
  • underweight for one's age

Prepositions

Etymology

Old EnglishEnglish

Formed by combining the Old English prefix 'under-' (meaning below or beneath) with 'weight,' which comes from the Old English 'gewiht' (meaning heaviness or measured mass). The compound was used from the 16th century to describe objects below expected weight, and by the late 1800s it became a standard medical term for people weighing less than what is considered healthy.