Webster's 1913 Dictionary
http://www.webster-dictionary.org/
It isn't Oxford, unfortunately, but I did find a Websters 1913 online. Tolkien was in college at that point. I think it sheds some light on his vocabulary choices.
Consider these exerpts:
cosmogonic - pertaining to the branch of astronomy dealing with the origin and history and structure and dynamics of the universe; "cosmologic science"; "cosmological redshift"; "cosmogonic theories of the origin of the universe"
Synonyms: cosmogenic, cosmogenical, cosmogonical, cosmologic, cosmological
SplenŽdor
n. 1. Great brightness; brilliant luster; brilliancy; as, the splendor ot the sun.
2. Magnifience; pomp; parade; as, the splendor of equipage, ceremonies, processions, and the like.
3. Brilliancy; glory; as, the splendor of a victory.
vast:
1. Waste; desert; desolate; lonely.
The empty, vast, and wandering air. - Shak.
2. Of great extent; very spacious or large; also, huge in bulk; immense; enormous; as, the vast ocean; vast mountains; the vast empire of Russia.
Through the vast and boundless deep. - Milton.
3. Very great in numbers, quantity, or amount; as, a vast army; a vast sum of money.
4. Very great in force; mighty; as, vast labor.
5. Very great in importance; as, a subject of vast concern.
high:
1. Elevated above any starting point of measurement, as a line, or surface; having altitude; lifted up; raised or extended in the direction of the zenith; lofty; tall; as, a high mountain, tower, tree; the sun is high.
2. Regarded as raised up or elevated; distinguished; remarkable; conspicuous; superior; - used indefinitely or relatively, and often in figurative senses, which are understood from the connection
3. Elevated in character or quality, whether moral or intellectual; preëminent; honorable; as, high aims, or motives.
NoŽble
a. 1. Possessing eminence, elevation, dignity, etc.; above whatever is low, mean, degrading, or dishonorable; magnanimous; as, a noble nature or action; a noble heart.
Statues, with winding ivy crowned, belong
To nobler poets for a nobler song. - Dryden.
2. Grand; stately; magnificent; splendid; as, a noble edifice.
Purged of the gross:
v. t. 1. To cleanse, clear, or purify by separating and carrying off whatever is impure, heterogeneous, foreign, or superfluous.
[imp. & p. p. Purged ; p. pr. & vb. n. Purging .]
...
5. To clear from guilt, or from moral or ceremonial defilement; as, to purge one of guilt or crime.
When that he hath purged you from sin. - Chaucer.
Purge me with hyssop, and I shall be clean.
gross - twelve dozen. Synonyms: 144. (Number of Hobbits invited to hear Bilbo's speech.)
More common definitions:
1. Great; large...
2. Coarse; rough; not fine or delicate.
3. Not easily aroused or excited; not sensitive in perception or feeling; dull; witless.
Tell her of things that no gross ear can hear. - Milton.
4. Expressing, or originating in, animal or sensual appetites; hence, coarse, vulgar, low, obscene, or impure.
The terms which are delicate in one age become gross in the next. - Macaulay.
5. Disgusting; repulsive; highly offensive; as, a gross remark.