Etymology
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latent (adj.)

mid-15c., "concealed, secret," from Latin latentem (nominative latens) "lying hid, concealed, secret, unknown," present participle of latere "lie hidden, lurk, be concealed," from PIE *late-, suffixed form of root *lādh- "to be hidden" (source also of Greek lēthē "forgetfulness, oblivion," lēthargos "forgetful," lathre "secretly, by stealth," lathrios "stealthy," lanthanein "to be hidden;" Old Church Slavonic lajati "to lie in wait for"). Meaning "dormant, undeveloped" is from 1680s, originally in medicine.

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latency (n.)
1630s, "condition of being concealed, unobserved existence," from latent + abstract noun suffix -cy. Meaning "delay between stimulus and response" is from 1882 (perhaps via the notion of "dormancy"); computer sense (latency time) is from 1954.
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latescent (adj.)
"tending to become latent or obscure, not obvious to perception," 1836, from Latin latescentem (nominative latescens), present participle of latescere "to hide oneself, be hidden," inchoative of latere "to lie hidden" (see latent). Related: Latescence.
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latebrous (adj.)
"full of hiding places," 1650s, from Latin latebrosus, from latebra "a hiding place," from latere "to lie hidden" (see latent). Hence latebricole "living or lurking in holes" (of spiders, etc.), from Latin latebricola "one who dwells in lurking places."
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Alethea 

fem. proper name, from Greek aletheia "truth, truthfulness," from alethes "true," literally "not concealing," from privative prefix a- "not" (see a- (3)) + lēthē "forgetfulness, oblivion, concealment," from PIE root *ladh- "be hidden" (see latent).

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lanthanum (n.)
metallic rare earth element, 1841, coined in Modern Latin by Swedish chemist and mineralogist Carl Gustav Mosander (1797-1858), who discovered it in 1839, from Greek lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). So called because the element was "concealed" in the earth from which he extracted it.
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Lethe 

mythical river of Hades (whose water when drunk caused forgetfulness of the past), in Homer, a place of oblivion in the lower world; from Greek lēthē, literally "forgetfulness, oblivion," from PIE root *ladh- "be hidden" (see latent). Related to lēthargos "forgetful" and cognate with Latin latere "to be hidden." Also the name of a personification of oblivion, a daughter of Eris. Related: Lethean.

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alastor (n.)

"In early Greek mythology, the spirit of revenge, that prompts the members of a family to commit fresh crimes to obtain satisfaction" [Encyclopaedia Britannica, 1941]. The name also was used of the evil genius which drives a man to sin and of a man so driven. A Greek word of uncertain origin. The traditional guess is that it is literally "the unforgetting," from a- "not" (see a- (3)) + root of lathein "to forget," aorist of lanthanein "to lie hidden, escape notice," from PIE root *ladh- "to be hidden" (see latent). Or else it might be connected with alaomai "to wander, roam," figuratively "to be distraught." As a proper name, in Greek tradition a son of Neleus and Chloris; brother of Nestor, he was slain by Herakles.

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lethargy (n.)

late 14c., litarge, "state of prolonged torpor or inactivity, inertness of body or mind," from Medieval Latin litargia, from Late Latin lethargia, from Greek lēthargia "forgetfulness," from lēthargos "forgetful," apparently etymologically "inactive through forgetfulness," from lēthē "a forgetting, forgetfulness" (see latent) + argos "idle" (see argon). The form with -th- is from 1590s in English. The Medieval Latin word also is the source of Old French litargie (Modern French léthargie), Spanish and Italian letargia.

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developer (n.)

1833, "one who or that which develops," agent noun from develop. Photography use in reference to the chemical bath used to bring out the latent image is attested from 1869; meaning "speculative builder" is by 1938.

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