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

Adjective

• featherlight
• feathery
• light
• lightweight
• weightless

Examples of underweight in a Sentence

Adjective

the long illness left him frail and underweight

Recent Examples on the Web

Adjective

But there were also broader losses in reading and math proficiency, lower preschool enrollment and a higher rate of babies born underweight. —Laura Tillman, Hartford Courant, 12 June 2025

Found as a stray last August, Gilly was dangerously underweight and had clearly been through a lot. —Tj MacIas, Kansas City Star, 9 June 2025

The Denver Animal Shelter is seeing a troubling rise in animal neglect cases, with a growing number of pets arriving dangerously underweight and weak. —Jessica Alvarado Gamez, Denver Post, 5 June 2025

Bumble — The dating app's stock lost 6% on the back of JPMorgan's downgrade to underweight from neutral. —Lisa Kailai Han, CNBC, 3 June 2025

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
• adsorbate
• aggravate
• agitate
• alginate
• alienate
• allocate
• amputate

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