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

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

Only 6% of people with eating disorders are considered medically underweight. — Erin Harrop, The Conversation, 18 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