Of an inappropriately or unusually lowweight.He's so underweight he's had to buy smaller clothes.He's thirty pounds underweight.
Not too heavy for an intended purpose.The suitcase is just slightly underweight; I'll let it on the plane.
(finance) Being less invested in a particular area than market wisdom suggests.The fund is underweight in mining.
2011, Murdoch, S. Foreigners back for Aussie stocks, The Australian"It's a long-run trend of foreign investors -- typically being underweight the banking sector in Australia," Mr Baker said.
1996, United States Institute of Medicine Committee on Scientific Evaluation of Nutrition Risk Criteria, WIC Nutrition Risk Criteria: A Scientific Assessment, National Academies Press, ISBN 978-0-309-05385-3, page 110,Underweight reflects the body’s thinness, but the term does not necessarily imply the nature and causes of underweight.