c. 1500, "loftiness, height," from French grandeur, from Old French grandor "size, height, extent, magnitude; greatness" (12c.), from grand "great" (see grand (adj.)). "Being a word of late adoption, it retains the Fr. form -eur of the suffix." Extended sense of "majesty, stateliness" in English is first recorded 1660s.
"act of misleading someone, deception, deceit," early 15c., delusioun, from Latin delusionem (nominative delusio) "a deceiving," noun of action from past-participle stem of deludere (see delude). As a form of mental derangement, "false impression or belief of a fixed nature," 1550s.
Technically, delusion is a belief that, though false, has been surrendered to and accepted by the whole mind as a truth; illusion is an impression that, though false, is entertained provisionally on the recommendation of the senses or the imagination, but awaits full acceptance and may not influence action. Delusions of grandeur, the exact phrase, is recorded from 1840, though the two words were in close association for some time before that.
"mental disorder characterized by systematized delusions of more or less definite scope," 1848 (earlier paranoea 1811), from Greek paranoia "mental derangement, madness," from paranoos "mentally ill, insane," from para- "beside, beyond" (see para- (1)) + noos "mind," which is of uncertain origin.
FOR several years frequent descriptions have been given in the foreign journals, especially German and Italian, of the forms of insanity designated by the names Paranoia, Verrücktkeit, and Wahnsinn. ["Paranoia — Systematized Delusions and Mental Degenerations," J. Séglas (transl. William Noyes), 1888]
mid-14c., "great-mindedness, courage," from Old French magnificence "splendor, nobility, grandeur," from Latin magnificentia "splendor, munificence," from stem of magnificus "great, elevated, noble, eminent," also "splendid, rich, fine, costly," literally "doing great deeds," from magnus "great" (from PIE root *meg- "great") + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").
Meaning "greatness of appearance or character, grandeur, glory" in English is from late 14c. That of "beauty, splendor, wealth" is 15c. As one of the Aristotelian and scholastic virtues, it translates Greek megaloprepeia "liberality of expenditure combined with good taste."
c. 1300, mageste, "greatness or grandeur of exalted rank or character, imposing loftiness, stateliness, qualities appropriate to rulership," from Old French majeste "grandeur, nobility" (12c.), from Latin maiestatem (nominative maiestas) "greatness, dignity, elevation, honor, excellence," from stem of maior (neuter maius), comparative of magnus "great, large, big" (of size), "abundant" (of quantity), "great, considerable" (of value), "strong, powerful" (of force); of persons, "elder, aged," also, figuratively, "great, mighty, grand, important," from suffixed form of PIE root *meg- "great."
Earliest English use is with reference to God or Christ; as a title of address or dignity to kings and queens (late 14c.), it is from Romance languages and originated in the Roman Empire.