The Hittite word a-ru-na-
Word a-ru-na-
IPA aruna
Meaning sea
Notes/Remarks The etymology of this word is unknown
See also Palaic: a-ru-na ‘sea’

Comments
There's no accepted etymology for it. Could be a Hattic loan, but there is no direct evidence for it.

Other words that might be of interest
ua-a-tar ‘water’, wa-a-tar ‘water’, lu-li-iš ‘pond, lake, spring, well, basin’, e-kan ‘cold, frost, ice’, ḫe-e-u- ‘rain’, ḫa-pa-aš ‘river’