Etymology
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imagination (n.)

"faculty of the mind which forms and manipulates images," mid-14c., ymaginacion, from Old French imaginacion "concept, mental picture; hallucination," from Latin imaginationem (nominative imaginatio) "imagination, a fancy," noun of action from past participle stem of imaginari "to form an image of, represent"), from imago "an image, a likeness," from stem of imitari "to copy, imitate" (from PIE root *aim- "to copy") 

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*aim- 

Proto-Indo-European root meaning "to copy." 

It forms all or part of: emulate; emulation; emulous;  image; imaginary; imagination; imaginative; imagine; imago; imitable; imitate; imitative; imitator; inimitable.

It is the hypothetical source of/evidence for its existence is provided by: Latin imago "image," aemulus "emulous," imitari "to copy, portray, imitate;" Hittite himma- "imitation, substitute."

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imaginative (adj.)
late 14c., ymaginatyf, "pertaining to imagination; forming images, given to imagining," from Old French imaginatif and directly from Medieval Latin imaginativus, from imaginat-, stem of Latin imaginari "picture to oneself" (see imagine). Meaning "resulting from imagination" is from 1829. Related: Imaginatively; imaginativeness.
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arresting (adj.)
1792, "stopping," present-participle adjective from arrest (v.). Figurative sense of "striking, that captures the imagination" is by 1883.
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dreamland (n.)

"land or region seen in dreams," hence "the land of fancy or imagination," 1827, from dream (n.) + land (n.).

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fictive (adj.)
1610s, "formed by imagination," from French fictif, from stem of Latin fictio (see fiction). Earlier as "convincingly deceptive" (late 15c.). Related: Fictively.
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fantasy (n.)

early 14c., "illusory appearance," from Old French fantaisie, phantasie "vision, imagination" (14c.), from Latin phantasia, from Greek phantasia "power of imagination; appearance, image, perception," from phantazesthai "picture to oneself," from phantos "visible," from phainesthai "appear," in late Greek "to imagine, have visions," related to phaos, phōs "light," phainein "to show, to bring to light" (from PIE root *bha- (1) "to shine").

Sense of "whimsical notion, illusion" is pre-1400, followed by that of "fantastic imagination," which is first attested 1530s. Sense of "day-dream based on desires" is from 1926. In early use in English also fantasie, phantasy, etc. As the name of a fiction genre, by 1948.

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ideally (adv.)
"in the best conceivable situation," 1840, from ideal + -ly (2). Earlier "in an archetype" (1640s); "in idea or imagination" (1590s).
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pretend (n.)

"act or fact of pretending in imagination or play," 1888, from children's talk, from pretend (v.). Earlier in same sense was the verbal noun pretending (1640s).

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flighty (adj.)
1550s, "swift," from flight (n.1) + -y (2). Sense of "fickle or frivolous" is from 1768, perhaps from notion of "given to 'flights' of imagination." Related: Flightiness.
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