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

Experts told the outlets that the eagle did not suffer any broken bones or serious injuries, but had been unable to fly and is underweight. — Kimberlee Speakman, PEOPLE, 21 July 2026

Some pups were weaned early or became underweight, and more than 4,000 young sea lions were found stranded along California beaches during peak years, overwhelming rehabilitation centers. — Brandi D. Addison, USA Today, 2 July 2026

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

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