ec·cen·tric·i·ty (?k?s?n-tr?s??-t?)n. pl. ec·cen·tric·i·ties 1. a. The quality of being eccentric.b. Deviation from the normal, expected, or established.2. An example or instance of eccentric behavior.3. Physics The distance between the center of an eccentric and its axis.4. Mathematics The ratio of the distance of any point on a conic section from a focus to its distance from the corresponding directrix. This ratio is constant for any particular conic section.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.eccentricity (??ks?n?tr?s?t?) n, pl -ties1. unconventional or irregular behaviour2. (Mathematics) deviation from a circular path or orbit3. (Astronomy) a measure of the noncircularity of an elliptical orbit, the distance between the foci divided by the length of the major axis4. (Mathematics) geometry a number that expresses the shape of a conic section: the ratio of the distance of a point on the curve from a fixed point (the focus) to the distance of the point from a fixed line (the directrix)5. (Mechanical Engineering) the degree of displacement of the geometric centre of a rotating part from the true centre, esp of the axis of rotation of a wheel or shaftCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ec?cen?tric?i?ty (??k s?n?tr?s ? ti, ??k s?n-) n., pl. -ties. 1. an oddity or peculiarity, as of conduct. 2. the quality of being eccentric. 3. the amount by which something is eccentric. 4. a mathematical constant expressed as the ratio of the distance from a point on a conic to a focus and the distance from the point to the directrix. [1545?55; (See also UNCONVENTIONALITY.)barmy on the crumpet Eccentric; a bit daft; wacko. This picturesque British expression plays on barmy ?balmy, foolish? and barmy ?yeasty??a crumpet being a breadlike muffin, here metaphorically standing for one?s head.have a moonflaw in the brain To be a lunatic; to behave in a very bizarre or peculiar manner. A moonflaw is an abnormality or idiosyncrasy ascribed to lunar influence. This now obsolete expression appeared in Brome?s Queen and Concubine (1652):I fear she has a moonflaw in her brains;She chides and fights that none can look upon her.have a screw loose To be eccentric, crotchety, or neurotic; to be irregular or amiss. As early as 1884, the phrase loose screw was used figuratively to apply to a flawed condition or state of affairs.I can see well enough there?s a screw loose in your affairs. (Charles Dickens, The Life and Adventures of Martin Chuzzlewit, 1884)A more recent and increasingly common figurative meaning applies have a screw loose to states of mind or mental health. This slang meaning is used in regard to whimsical, unusual behavior rather than to disturbed or sick behavior, although the phrase tends to conjure up images of ?falling apart? or ?breaking down.? A British variant is have a tile loose.have bats in one?s belfry To be eccentric, bizarre, crazy, daft. The erratic flight of bats in bell towers interferes with the proper ringing and tone of the bells, just as crazy notions darting about one?s brain weaken its ability to function. The slang term batty is a derivative of this phrase, which appeared as early as 1901 in a novel of G. W. Peck:They all thought a crazy man with bats in his belfry had got loose. (Peck?s Red-Haired Boy)The analogy between sanity and finely tuned bells is an old one; its most famous expression is in Ophelia?s description of the ?mad? Hamlet:Now see that noble and most sovereign reason,Like sweet bells jangled, out of tune and harsh. (III, i)off one?s trolley Crazy, demented; in a confused or befuddled state of mind; ill-advised; senile. This expression alludes to the once-common spectacle of a motorman?s attempts to realign the contact wheel of a trolley car with the overhead wire. Since this contact wheel is also called a ?trolley,? off one?s trolley may refer either to the conductor?s actions or to the fact that when the wires are ?off the trolley,? the vehicle no longer receives an electric current and is, therefore, rendered inoperative.The medium is clear off her trolley, for my father has been dead [for] three years. (Warren Davenport, Butte and Montana Beneath the X-Ray, 1908)A similar expression is slip one?s trolley ?to become demented.? In the more widely used variation, off one?s rocker, rocker is most often said to refer to the curved piece of wood on which a cradle or chair rocks. But since both off one?s trolley and off one?s rocker became popular about the time streetcars were installed in major American cities, and since rocker, like trolley, also means the wheel or runner that makes contact with an overhead electricity supply, it is more likely that the rocker of the expression carries this latter meaning.When asked if he had swallowed the liniment, he said, ?Yes, I was off my rocker.? (Daily News, June 29, 1897)queer in the attic Eccentric or feebleminded; intoxicated. In this expression, attic carries its British slang meaning of ?the mind?; thus, this colloquialism alludes to stupidity, insanity, or drunkenness, all of which may generate bizarre behavior.round the bend Insane, crazy. In this British expression, bend describes one?s mental faculties as being ?out of alignment, bent, or out of kilter.?Right round the bend ? I mean ? as mad as a hatter. (John I. M. Stewart, The Guardian, 1955)Related expressions are go round the bend and be driven round the bend.