adj

• (finance) Being less invested in a particular area than market wisdom suggests.
  "The fund is underweight in mining."

noun

• (uncountable) The state or quality of being underweight.
  "1996, United States Institute of Medicine Committee on Scientific Evaluation of WIC Nutrition Risk Criteria, WIC Nutrition Risk Criteria: A Scientific Assessment, National Academies Press, →ISBN, page 110, Underweight reflects the body’s thinness, but the term does not necessarily imply the nature and causes of underweight."
• (countable) An underweight person.
• (countable, finance) An underweight investment.
  "Further, structured managers usually attempt to hit their lower targets by relying on a relatively large number of small active deviations (i.e., overweights and underweights)."

verb

• (transitive) To underestimate the weight of.
• (transitive) To give insufficient weight to (a consideration); to underestimate the importance of.
• (transitive, finance) To invest in less than conventional wisdom would dictate.
  "Although the portfolio overweights the German market, it underweights German marks."