"no thing, not any thing, not something," Middle English, from Old English naþing, naðinc, from nan "not one" (see none) + þing "thing" (see thing). Meaning "insignificant thing, thing of no consequence" is from c. 1600. As an adverb, "not at all, in no degree," late Old English. As an adjective by 1961. For nothing "not at all" is from c. 1300. Nothing to it, indicating something easy to do, is by 1925. Nothing to write home about, indicating an unremarkable circumstance or thing, is from 1917 among the World War I soldiers.
1680s, "one who rejects the doctrine of the Trinity," from Modern Latin unitarius (1650s), from Latin unitas (see unity) + -ian. Applied to Muslims and other non-Christian monotheists, but especially (and with a capital -u-) of a Christian body originally founded upon the doctrine of unipersonality. The American Unitarian Association formed in 1825. As an adjective from 1680s.