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

• lightweight

Examples of underweight in a Sentence

Adjective

the long illness left him frail and underweight

Recent Examples on the Web

Adjective

Here are the biggest calls on Wall Street on Friday: Morgan Stanley upgrades Novartis to equal weight from underweight Morgan Stanley said in its upgrade of Novartis that growth is improving at the biopharma company. —Michael Bloom, CNBC, 8 Aug. 2025

The nurses down the hall don’t have neonatal incubators, which are the standard treatment for underweight babies born in the rich places of the world. —Literary Hub, 8 Aug. 2025

Child stunting and food insecurity levels fell, while adult obesity went up: Since 2016, there have been more obese people worldwide than underweight ones. —Tom Chivers, semafor.com, 4 Aug. 2025

Paris' vet exam revealed the dog has conjunctivitis, which she is being treated for, and is underweight. —Kelli Bender, People.com, 31 July 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