underweight

Short definition from Wiktionary

Adjective

1. 1
   Of an inappropriately or unusually low weight.
2. 2
   Not too heavy for an intended purpose.
3. 3
   Being less invested in a particular area than market wisdom suggests.

Noun

1. 1
   The state or quality of being underweight.
2. 2
   An underweight person.
3. 3
   An underweight investment.

Verb

1. 1
   To underestimate the weight of.
2. 2
   To give insufficient weight to (a consideration); to underestimate the importance of.
3. 3
   To invest in less than conventional wisdom would dictate.