›[I or T]ACCOUNTING, FINANCEto say that you have done, earned, sold, etc., less than you really have: Some of the companies clearly underreport.They underreported revenues to secure public money for new stadiums.
›[T]USTAXto record that you have earned less than you really have on your tax return (= a document in which income is reported each year so tax can be calculated): He under-reported his income by $548,000.