to report fewer than the actual number or less than the true amount of
transitive verbun·der·re·port·ed, un·der·re·port·ing, un·der·re·ports
To report (income or crime statistics, for example) as being less than actually is the case.
(third-person singular simple present underreports, present participle underreporting, simple past and past participle underreported)
under- +"Ž report.