underwrite v.

Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (source also of Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (source also of Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").

Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).

Under the weather "indisposed" is from 1810. Under the table is from 1913 in the sense of "very drunk," 1940s in sense of "illegal" (under-board "dishonest" is from c. 1600). To keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832.

Old English writan "to score, outline, draw the figure of," later "to set down in writing" (class I strong verb; past tense wrat, past participle writen), from Proto-Germanic *writan "tear, scratch" (source also of Old Frisian writa "to write," Old Saxon writan "to tear, scratch, write," Old Norse rita "write, scratch, outline," Old High German rizan "to write, scratch, tear," German reißen "to tear, pull, tug, sketch, draw, design"), outside connections doubtful.

For men use to write an evill turne in marble stone, but a good turne in the dust. [More, 1513]

Words for "write" in most Indo-European languages originally mean "carve, scratch, cut" (such as Latin scribere, Greek graphein, glyphein, Sanskrit rikh-); a few originally meant "paint" (Gothic meljan, Old Church Slavonic pisati, and most of the modern Slavic cognates). To write (something) off (1680s) originally was from accounting; figurative sense is recorded from 1889. Write-in "unlisted candidate" is recorded from 1932.