I looked up "lava" in the Digital Pali Reader (developed by Yuddhammo bhikkhu).

ละวะ

lava: a drop. (m.)

Lava [fr. lū] a small particle, a drop VvA 253 (lavanka a small mark); Sdhp 105 (˚odaka).

อุทัย

udaya: rise; growth; increase; income; interest (from money). (m.)

It is puzzling what context a "small drop" could be big enough to name a kingdom after (???).

-- a small rising?

-- 'from little things, big things grow'?

PS.

ละวะ -->ละพะ --> ลพ as in ลพบุรี [purii, pura: a town or city. (nt.)]