late 13c., conceiven, "take (seed) into the womb, become pregnant," from stem of Old French conceveir (Modern French concevoir), from Latin concipere (past participle conceptus) "to take in and hold; become pregnant" (source also of Spanish concebir, Portuguese concebre, Italian concepere), from con-, here perhaps an intensive prefix (see con-), + combining form of capere "to take" (from PIE root *kap- "to grasp").

Meaning "take into the mind, form a correct notion of" is from mid-14c., that of "form as a general notion in the mind" is from late 14c., figurative senses also found in the Old French and Latin words. Related: Conceived; conceiving.

Nearly all the senses found in Fr. and Eng. were already developed in L., where the primary notion was app. 'to take effectively, take to oneself, take in and hold'. [OED]

"capable of being thought or supposed," mid-15c., from conceive + -able. Related: Conceivably; conceivability; conceivableness.

late 14c., "to have a wrong notion of, misunderstand," from mis- (1) "badly, wrongly" + conceive. Related: Misconceived; misconceiving.

"form a conception, notion, or idea of in advance of actual knowledge," 1570s, from pre- "before" + conceive. Related: Preconceived; preconceiving; preconceit.

1630s, "capable of conceiving mentally;" 1640s, "capable of conceiving physically;" from Latin conceptivus, from concept-, past participle stem of concipere "to take in" (see conceive). Shakespeare used conceptious "fruitful."

c. 1600, "having an overweening opinion of oneself" (short for self-conceited, 1590s), past-participle adjective from conceit (v.) "conceive, imagine, think" (1550s), a now-obsolete verb from conceit (n.). Earlier it meant "having intelligence, ingenious, witty" (1540s). Related: Conceitedly; conceitedness.

"pertaining to mental conception," 1820 (there is an isolated use from 1662), from Medieval Latin conceptualis, from Latin conceptus "a collecting, gathering, conceiving," past participle of concipere "to take in" (see conceive). Perhaps it emerged to go with the distinctly mental sense of conception, as it seems rarely, if ever, to have been used in the physical sense. Conceptional "pertaining to or having the nature of (physical) conception" is from 1832.

late 14c., "a thought, a notion, that which is mentally conceived," from conceiven (see conceive) based on analogy of deceit/deceive and receipt/receive. The sense evolved from "something formed in the mind" to "fanciful or witty notion, ingenious thought" (1510s), to "vanity, exaggerated estimate of one's own mental abilities" (c. 1600) through shortening of self-conceit (1580s).

A doublet of concept, it sometimes was spelled conceipt in Middle English. Sometimes the Italian form concetto (plural concetti) was used in English 18c.-19c. for "piece of affected wit;" OED describes it as "a term originally proper to Italian literature."

Old English þoht, geþoht "process of thinking, a thought; compassion," from stem of þencan "to conceive of in the mind, consider" (see think). Cognate with the second element in German Gedächtnis "memory," Andacht "attention, devotion," Bedacht "consideration, deliberation."

Bammesberger ("English Etymology") explains that in Germanic -kt- generally shifted to -ht-, and a nasal before -ht- was lost. Proto-Germanic *thankija- added a suffix -t in the past tense. By the first pattern the Germanic form was *thanht-, by the second the Old English was þoht.

Second thought "later consideration" is recorded from 1640s. Thought-crime is from "Nineteen Eighty-Four" (1949); thought police is attested from 1945, originally in reference to war-time Japanese Special Higher Police (Tokubetsu Koto Keisatsu).

"calm, quiet, peaceful," 1540s, in halcyon dayes (translating Latin alcyonei dies, Greek alkyonides hemerai), 14 days of calm weather at the winter solstice, when a mythical bird (also identified with the kingfisher) was said to breed in a nest floating on calm seas. The name of this fabulous bird is attested in Middle English as alcioun (late 14c.).

The name is from Latin halcyon, alcyon, from Greek halkyon, variant (perhaps a misspelling) of alkyon "kingfisher," a word of unknown origin. The explanation that this is from hals "sea; salt" (see halo-) + kyon "conceiving," present participle of kyein "to conceive," literally "to swell" (see cumulus) probably is ancient folk-etymology to explain a loan-word from a non-Indo-European language. Identified in mythology with Halcyone, daughter of Aeolus, who when widowed threw herself into the sea and became a kingfisher.