lacunary (adjective): from Latin lacuna “a ditch, pit, hole, pool, pond,” from lacus “a hollow thing,” and therefore “a basin, tank, tub.” The Indo-European root is laku- “body of water, lake,” as seen in our words lake and lagoon, borrowed ultimately from Latin. As used in nonmathematical English, lacuna emphasizes the “hole” meaning of the Latin word rather than the “pool” meaning. In mathematics, a lacunary function is an analytic function represented by a circle with a natural boundary; that circle represents a “lake” on which the function converges.

lambda (noun): eleventh letter of the Greek alphabet, written ∧ as a capital and λ in lower case. It corresponds to the Hebrew letter lamedh, meaning “ox goad,” and to the sound of our letter l. Looking at the Hebrew letter, it is not hard to imagine an ox goad; the Greek letter is a bit further removed in shape from the original object. See further explanation under aleph. In calculus λ is used to stand for a Lagrange multiplier because the first letter in Lagrange is an L.

lamina (noun): a Latin word meaning “a thin piece of metal or wood, a flat plate.” The Indo-European root may be stelə- “to extend.” From the Latin word, after many modifications in French, comes omelette, which is flat.When a document is laminated, it is encased in a thin, flat plastic covering. A common type of calculus problem involves finding the centroid of a lamina. [210]