A Elbereth Gilthoniel
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!- Na-chaered palan-díriel- 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.