type of mineral that can be separated easily into extremely thin, tough laminae, 1706, from a Modern Latin specialized use of Latin mica "crumb, bit, morsel, grain."  This is sometimes said to be from the same source as Attic Greek mikros "small" (see micro-). The word was applied to the mineral probably on the supposition that it was related to Latin micare "to flash, glitter" (see micacious). However a recent theory of the origin of the Latin noun does derive it from the same root as micare, on the notion of "a glittering crystalline particle" (originally a grain of salt), which de Vaan finds "formally more attractive" than the connection to the Greek word. Older native names for it were glimmer and cat-silver. Related: Micaceous "containing mica" (1748).

popular name for a bacterium or other extremely small living being, 1878, from French microbe, "badly coined ... by Sédillot" [Weekley] in 1878 from Latinized form of Greek mikros "small" (see micro-) + bios "life" (from PIE root *gwei- "to live"). Intended to mean literally "a small living being," the use of bios is incorrect, as in modern science generally (see bio-); in Greek the compound would mean "short-lived."

"the science of micro-organisms," 1880, coined in English from micro- + biology. Related: Microbiological.

"small-headed, having an unusually small cranium," either as measured against a certain standard or through disease or faulty development, 1845, from French microcéphalique, from Modern Latin microcephalus, from Greek mikros "small" (see micro-) + kephalē "head" (see cephalo-). Related: Microcephalism; microcephalous (1840); microcephaly (n.).

in computing, "integrated circuit," 1975, from micro- + chip (n.1) in the computing sense.

also micro-circuit, in electronics, "integrated circuit," 1959, from micro- + circuit (n.). Related: Microcircuitry.

"climate of a very small or restricted area," 1918, from micro- + climate. Related: Microclimatology; microclimatological.

"small computer built around a single microprocessor," 1971, from micro- + computer. A name for what later generally would be called a personal or home computer.

late 12c., mycrocossmos (modern form from early 15c.), "human nature, man viewed as the epitome of creation," literally "miniature world" (applied metaphorically to the human frame by philosophers, hence a favorite word with medieval writers to signify "a man"), from Medieval Latin microcosmus, from Greek mikros "small" (see micro-) + kosmos "world" (see cosmos).

General sense of "a community constituting a world unto itself, a little society" is attested from 1560s, perhaps from French microcosme. A native expression in the same sense was petty world (c. 1600).

Forrþi mahht tu nemmnenn mann Affterr Grikkishe spæche Mycrocossmos, þat nemmnedd iss Affterr Ennglisshe spæche Þe little werelld. ["Ormulum," c. 1175]

And the Anglo-Saxon glossaries have læsse middaneard.

"tiny capsule of LSD," by 1971, from micro- + dot (n.). Earlier it was a term in espionage for an extremely reduced photograph that could be disguised as a period dot on a typewritten manuscript (by 1946).