o·me·ga 
(ō-mĕgə, ō-mēgə, ō-mā-)
(ō-mĕgə, ō-mēgə, ō-mā-)n.
1. The 24th letter of the Greek alphabet. See Table at alphabet.
2. The last of a series; the end.
3. In cosmology theory, the ratio of the average density of matter in the universe to its critical density.
4. See omega baryon.
5. See omega meson.
adj.
Chemistry
Chemistry
Relating to the end of the chain of carbon atoms that is opposite the carboxyl group in the molecule of a fatty acid.
[Middle English, from Greek ō mega, large o (from its being a long vowel in Greek) : ō, the letter o + mega, neuter of megas, large, great; see meg- in the Appendix of Indo-European roots.]