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

Obesity can disrupt the body's metabolism, weaken the immune system and lead to diseases like Type 2 diabetes, cardiovascular diseases and up to 15 different cancers, while being underweight is tied to malnutrition, weakened immunity and nutrient deficiencies, Gribsholt warned. —Deirdre Bardolf, FOXNews.com, 20 Sep. 2025

This rally has likely been unwelcome for managers who remain underweight in Chinese stocks. —Brendan Ahern, Forbes.com, 16 Sep. 2025

Contrary to popular assumptions, children experiencing food insecurity do not necessarily appear underweight. —Oona Hanson, CNN Money, 16 Sep. 2025

Being obese is more prevalent than being underweight in all regions of the world except sub-Saharan Africa and South Asia. —Tom Chivers, semafor.com, 10 Sep. 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