swalda : forests
The Illunse word for forests (plural) is swalda. The word for forest is swald. Swalda (or Sualda) was king of Meirionydd in Wales in the early 7th century.
Forests in Latin is silvae. Forests in Old English is wealda.
I've changed this word. My Illunse word for forests is now seldu.
feama : rivers
The Illunse word for rivers (plural) is feama. The word for river is feam. Feama is a rare first name.
Rivers in Latin is flumenis. Rivers in Old English is éa.
Here are two more nominative case plurals. In this case, the plurals were formed by adding -a.