Etymology
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mensa (n.)

"altar top," 1848, Latin, literally "table," also "meal, supper," and "altar, sacrificial table," hence used in Church Latin for "upper slab of a church altar" (see mesa). With a capital M-, the name of an organization for people of IQs of 148 or more founded in England in 1946, the name chosen, according to the organization, to suggest a "round table" type group. The constellation (1763) originally was Mons Mensae "Table Mountain." It is the faintest constellation in the sky, with no star brighter than magnitude 5.0.

La Caille, who did so much for our knowledge of the southern heavens, formed the figure from stars under the Greater Cloud, between the poles of the equator and the ecliptic, just north of the polar Octans; the title being suggested by the fact that the Table Mountain, back of Cape Town, "which had witnessed his nightly vigils and daily toils," also was frequently capped by a cloud. [Richard Hinckley Allen, "Star Names and Their Meanings," London: 1899]
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table (n.)

late 12c., "board, slab, plate," from Old French table "board, square panel, plank; writing table; picture; food, fare" (11c.), and late Old English tabele "writing tablet, gaming table," from Germanic *tabal (source also of Dutch tafel, Danish tavle, Old High German zabel "board, plank," German Tafel). Both the French and Germanic words are from Latin tabula "a board, plank; writing table; list, schedule; picture, painted panel," originally "small flat slab or piece" usually for inscriptions or for games (source also of Spanish tabla, Italian tavola), of uncertain origin, related to Umbrian tafle "on the board."

The sense of "piece of furniture with the flat top and legs" first recorded c. 1300 (the usual Latin word for this was mensa (see mensa); Old English writers used bord (see board (n.1)). Especially the table at which people eat, hence "food placed upon a table" (c. 1400 in English). The meaning "arrangement of numbers or other figures on a tabular surface for convenience" is recorded from late 14c. (as in table of contents, mid-15c.).

Figurative phrase turn the tables (1630s) is from backgammon (in Old and Middle English the game was called tables). Table talk "familiar conversation around a table" is attested from 1560s, translating Latin colloquia mensalis. Table manners is from 1824. Table-hopping is recorded by 1943. The adjectival phrase under-the-table "hidden from view" is recorded from 1949; to be under the table "passed out from excess drinking" is recorded from 1913. Table tennis "ping-pong" is recorded from 1887. Table-rapping in spiritualism, supposedly an effect of supernatural powers, is from 1853.

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mensal (adj.2)
"pertaining to or used at a table," mid-15c., from Late Latin mensalis, from Latin mensa "table" (see mesa).
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commensal (adj.)

late 14c., "eating together at the same table, sharing the table with the host," from Medieval Latin commensalis, from com "with, together" (see com-) + mensa (genitive mensalis) "table" (see mesa). 

As a noun, "one who eats at the same table" (as another), early 15c. Biological sense "one of two animals or plants which live together but neither at the expense of the other" is attested from 1870.

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mesa (n.)

"high table land, in the U.S. Southwest, a broad and flat region between canyons or rivers," 1759, from Spanish mesa "plateau," literally "table," from Latin mensa "table" for sacred offerings or for meals (source of Romanian masa, Old French moise "table"), which de Vaan writes is probably the feminine of the past participle mensus ("measured") of metiri (from PIE root *me- (2) "to measure"),formed by analogy with pensus "weighed."  He compares Umbrian mefa, mefe, name of a certain sacrificial object, perhaps cake, and writes, "In Latin, the meaning then shifted from the offering itself to the object on which the offerings were placed."

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mensal (adj.1)
"monthly," 1860, from Latin mensis "month" (see moon (n.)) + -al (1).
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