Etymology
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lank (adj.)

Old English hlanc "loose and empty, meagerly slim, flaccid," from Proto-Germanic *hlanka-, forming words meaning "to bend, turn," perhaps from PIE root *kleng- "to bend, turn," with a connecting notion of "flexible" (compare German lenken "to bend, turn aside;" see flank (n.)). In Middle English, "Some examples may be long adj. with unvoicing of g" [The Middle English Compendium]. In reference to hair, "straight and flat," from 1680s. Related: Lankness (1640s).

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lanky (adj.)
1630s, "straight and flat," used of hair, from lank (adj.) + -y (2). Sense of "awkwardly tall and thin" is first recorded 1818. Fowler writes that "The short form is almost only literary, the long chiefly colloquial." Related: Lankily (1848); lankiness (1846).
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link (n.)
early 15c., "one of a series of rings or loops which form a chain; section of a cord," probably from Old Norse *hlenkr or a similar Scandinavian source (compare Old Norse hlekkr "link," in plural, "chain;" Old Swedish lænker "chain, link," Norwegian lenke "a link," Danish lænke "a chain," German Gelenk "articulation, a joint of the body; a link, ring"), from Proto-Germanic *khlink- (source also of German lenken "to bend, turn, lead"), from PIE root *kleng- "to bend, turn." Related to lank, flank, flinch.

The noun is not found in Old English, where it is represented by lank "the hip" ("turn of the body"), hlencan (plural) "armor." Meaning "a division of a sausage made in a continuous chain" is from mid-15c. Meaning "anything serving to connect one thing or part with another" is from 1540s. Sense of "means of telecommunication between two points" is from 1911. Missing link between man and apes dates to 1880.
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leio- 
scientific word-forming element meaning "smooth," from Greek leios "smooth, level, flat; plain, unembroidered; beardless." E.g. leiotrichy, in ethnology, of races, "condition of having straight, lank hair" (1924).
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sheep-shank (n.)
also sheepshank, 1670s, "leg of a sheep," from sheep + shank (n.). A type of something lank, slender, or weak. Attested earlier in transferred sense of "type of sailor's knot used to shorten a rope without cutting it" (1620s).
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rat-tail (n.)

also rat's-tail, from rat (n.) + tail (n.1). Used since 16c. of conditions, growths, or devices held to resemble a rat's long, hairless tail in any way, including "lank lock of hair" (1810); "end of a rope" (1867). Related: Rat-tailed. A rat-tail file (1744) is a fine, round file used for enlarging holes in metal.

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slab (n.)
late 13c., "large, flat mass," of unknown origin, possibly related to Old French escopel, escalpe "thin fragment of wood," which according to Klein is possibly a Gaulish word (compare Breton scolp, Welsh ysgolp "splinter, chip"). But OED rejects this on formal grounds. Meaning "rectangular block of pre-cast concrete used in building" is from 1927. Slab-sided is "having flat sides like slabs," hence "tall and lank" (1817, American English).
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twitter (v.)

late 14c., twiteren, in reference to birds, of imitative origin (compare Old High German zwizziron, German zwitschern, Danish kvidre, Old Swedish kvitra). The noun meaning "condition of tremulous excitement" is attested from 1670s. The microblogging service with the 140-character limit was introduced in 2006. The following is considered an unrelated word of obscure origin:

TWITTER. 1. "That part of a thread that is spun too small." Yarn is said to be twined to twitters, when twined too small, S. Hence, to twitter yarn, to spin it unequally, A. Bor. Ray.
2. It is transferred to any person or thing that is slender or feeble. It is said of a lank delicate girl: "She is a mere twitter," S. [Jamieson, "Etymological Dictionary of the Scottish Language," Edinburgh, 1808]
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Sri Lanka 
large island southeast of India (known in English until 1972 as Ceylon), from Lanka, older name for the island and its chief city, + Sanskrit sri "beauty" (especially of divinities, kings, heroes, etc.), also an honorific prefix to proper names, from PIE root *kreie- "to be outstanding, brilliant, masterly, beautiful," found in Greek (kreon "lord, master") and Indo-Iranian.
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