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

The district attorney’s office said the child was reported to smell like cat urine and appeared seriously underweight and pale. — Los Angeles Times, 14 Oct. 2026

About two-thirds of Gaza’s people are thought to be malnourished; as many as seven in ten babies are born underweight. — Dexter Filkins, New Yorker, 14 Sep. 2026

The study also found a particularly high mortality risk among older adults who were underweight. — Faye Chiu, CNN Money, 26 Aug. 2026

Some of the dogs were significantly underweight and dehydrated, Animal Services reported. — Kendrick Calfee, Kansas City Star, 21 Aug. 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