underweight

1 of 2

noun

un·​der·​weight ˌən-dər-ˈwāt 

: weight below normal, average, or requisite weight

underweight

2 of 2

adjective

: weighing less than the normal or requisite amount

Synonyms of underweight

Adjective

• lightweight

Examples of underweight in a Sentence

Adjective

the long illness left him frail and underweight

Recent Examples on the Web

Adjective

When the 13 siblings were rescued, all but the 2-year-old were severely underweight and hadn’t bathed for months. — ABC News, 2 July 2026

Authorities said many of the dogs suffered from severe flea infestation, and some of the pups were underweight. — Leonard Greene, New York Daily News, 19 June 2026

Upon arrival, several of them were in critical condition and others were underweight with digestive issues. — Richard Tribou, The Orlando Sentinel, 16 June 2026

The compute build for inference has multi-year lead times, the capacity is already spoken for through 2027, and the buyers are still underweight. — Jon Markman, Forbes.com, 14 May 2026

Word History

First Known Use

Noun

1596, in the meaning defined above

Adjective

1675, in the meaning defined above

Rhymes for underweight

• abdicate
• abrogate
• acetate
• activate
• actuate
• aggravate
• agitate
• alginate
• alienate
• allocate
• amputate
• angulate

Kids Definition

underweight

adjective

un·​der·​weight

ˌən-dər-ˈwāt

: weighing less than what is normal, average, or necessary

Medical Definition

underweight

adjective

un·​der·​weight -ˈwāt 

: weighing less than the normal amount for one's age, height, and build

underweight children

underweight adults typically have a body mass index of less than 18.5