From Hindupedia, the Hindu Encyclopedia
By M. A. Alwar
Ūnaviṃśa means one less than 20, that is number 19.
Ūnaviṃśa can be used in all the three genders.
Ūnaviṃśa has been referred in the jyotistattvam as:
“The divisions of a day are eleven, nineteen and so on”.
- Shabdakalpadrumah by Raja Radhakantdev, Varadaprasada Vasu, Haricarana Vasu