Etymology
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gemination (n.)

1590s, "a doubling," from Latin geminationem (nominative geminatio) "a doubling," noun of action from past-participle stem of geminare "to double, repeat" (see geminate). In rhetoric, repetition of a word or phrase for emphasis.

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duplicative (adj.)

"having the quality of duplicating or doubling," 1854; see duplicate (v.) + -ive.

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LL. 

contraction of Latin legum "of laws, in degrees;" as in LL.D., which stands for Legum Doctor "Doctor of Laws." Plural abbreviations in Latin were formed by doubling the letter.

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duplication (n.)

early 15c., "act of doubling," from Old French duplicacion (13c.) and directly from Latin duplicationem (nominative duplicatio), noun of action from past-participle stem of duplicare "to double" (see duplicate (adj.)). Sense of "act of making or repeating something essentially the same" is from 1580s. Meaning "a duplicate copy or version" is by 1872.

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plait (n.)

late 14c., pleit, "a fold, a crease, a flattened gather made by doubling cloth or similar fabric in narrow strips upon itself," also "interlaced strands of hair," from Anglo-French pleit, Old French ploit, earlier pleit, "fold, manner of folding," from Latin plicatus, past participle of plicare "to lay, fold, twist" (from PIE root *plek- "to plait").

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crease (n.)

1660s, "long or thin mark made by doubling or folding," altered from creaste "a ridge," perhaps a variant of crest (n.), via meaning "a fold in a length of cloth" (mid-15c.) which produces a "crest." In sports, first in cricket (1779), where originally it was cut into the ground. As a verb, "to make creases in," from 1580s. Related: Creased; creasing.

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ap- (1)

form of Latin ad- in compounds with words or stems beginning in -p-; see ad-. In Old French reduced to a-, but scribal re-doubling of ap- to app- in imitation of Latin began 14c. in France, 15c. in England, and was extended to some compounds formed in Old French or Middle English that never had a Latin original (appoint, appall).

In words from Greek, ap- is the form of apo before a vowel (see apo-).

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reduplication (n.)

early 15c., "a turn back, a bend," a sense now obsolete; 1580s, "act of redoubling or repeating; state of being reduplicated," from French réduplication (16c.) and directly from Medieval Latin reduplicationem (nominative reduplicatio), noun of action from past-participle stem of reduplicare "to redouble," from re- "back, again" (see re-) + Latin duplicare "to double" (see duplicate (adj.)).

From 1640s as "act of reduplicating, doubling, or repeating;" specifically in philology, "repetition of a syllable or part of a syllable," by 1774.

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loop (n.)

late 14c., "a fold or doubling of cloth, rope, leather, cord, etc.," of uncertain origin. OED favors a Celtic origin (compare Gaelic lub "bend," Irish lubiam), which in English was perhaps influenced by or blended with Old Norse hlaup "a leap, run" (see leap (v.)). As a feature of a fingerprint, 1880. In reference to magnetic recording tape or film, first recorded 1931. Computer programming sense "sequence of instructions executed repeatedly" first attested 1947.

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double (v.)

c. 1200, doublen, "to make double; increase, enlarge, or extend by adding an equal portion, measure, or value to," from Old French dobler, from Latin duplare, from duplus "twofold, twice as much" (see double (adj.)). Intransitive sense of "to become twice as great" is from late 14c.

From mid-14c. as "to duplicate;" from late 14c. as "to repeat, do twice;" from c. 1400 in the transitive sense of "lay or fold one part of upon another." By 1540s as "to pass round or by." Sense of "turn in the opposite direction" is from 1590s. Meaning "to bend or fold" (a part of the body) is from early 15c.; to double up bodily is from 1814.

A blow on the stomach "doubles up" the boxer, and occasions that gasping and crowing which sufficiently indicate the cause of the injury .... [Donald Walker, "Defensive Exercises," 1840]

Meaning "to work as, in addition to one's regular job" is c. 1920, circus slang, from performers who also played in the band. Related: Doubled; doubling.

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