A Elbereth Gilthoniel is an aerlinn (poem) of Rivendell addressed to Varda, sung in Sindarin and in iambic tetrameter. The first stanza (the only one known) rhymes aababcc.
A Elbereth Gilthoniel-
Silivren penna míriel-
o menel aglar elenath!-
o galadhremmin Ennorath,-
Fanuilos, le linnathon-
nef aear, si nef Aearon.
Which translates as
O Elbereth Starkindler-
(white) glittering slants down-
sparkling like jewels-
from [the] firmament [the] glory [of] the star-host!-
To-remote distance far-having gazed -
from [the] tree-tangled middle-lands,-
Fanuilos, to thee I will chant-
on this side of ocean, here on this side of the Great Ocean!
The rest of it is not saved but it is possible that 'Oh Snowhite' is a Westron translation or variation of this aerlinn.