a. [ Pref. bi- + pyramidal. ] Consisting of two pyramids placed base to base; having a pyramid at each of the extremities of a prism, as in quartz crystals. [ 1913 Webster ]

n. [ Macro- + pyramid. ] (Crystallog.) See Macroprism. [ 1913 Webster ]

n. [ L. pyramis, -idis, fr. Gr. &unr_;, &unr_;, of Egyptian origin: cf. F. pyramide. ] [ 1913 Webster ]

1. A solid body standing on a triangular, square, or polygonal base, and terminating in a point at the top; especially, a structure or edifice of this shape. [ 1913 Webster ]

2. (Geom.) A solid figure contained by a plane rectilineal figure as base and several triangles which have a common vertex and whose bases are sides of the base. [ 1913 Webster ]

3. pl. (Billiards) The game of pool in which the balls are placed in the form of a triangle at spot. [ Eng. ] [ 1913 Webster ]

4. (Finance) a fraudulent investment scheme in which the manager promises high profits, but instead of investing the money in a genuine profit-making activity, uses the money from later investors to pay the profits to earlier investors; -- also called pyramid scheme or pyramid operation. This process inevitably collapses when insufficient new investors are available, leaving the later investors with total or near-total losses of their investments. The managers usually blame government regulations or interference for the collapse of the scheme, rather than admit fraud. [ PJC ]

Altitude of a pyramid (Geom.), the perpendicular distance from the vertex to the plane of the base. --
Axis of a pyramid (Geom.), a straight line drawn from the vertex to the center of the base. --
Earth pyramid. (Geol.) See Earth pillars, under Earth. --
Right pyramid (Geom.) a pyramid whose axis is perpendicular to the base. [ 1913 Webster ]

v. i. (Speculation) To enlarge one's holding or interest in a series of operations on a continued rise or decline by using the profits to buy or sell additional amounts on a margin, as where one buys on a 10% margin 100 shares of stock quoted at 100, holds it till it rises to 105, and then uses the paper profit to buy 50 shares more, etc. The series of operations constitutes a pyramid. A similar process of reinvesting gains or winnings (as of a gamble), but not involving operation on margin, is called a parlay. [ Webster 1913 Suppl. +PJC ]

v. t. (Speculation) To use, or to deal in, in a pyramiding transaction. See Pyramid, v. i. [ Webster 1913 Suppl. ]

n. (Anat.) One of the carpal bones. See Cuneiform, n., 2 (b). [ 1913 Webster ]

a. [ Cf. F. pyramidal. ] [ 1913 Webster ]

1. Of or pertaining to a pyramid; in the form of a a pyramid; pyramidical; as, pyramidal cleavage. [ 1913 Webster ]

The mystic obelisks stand up
Triangular, pyramidal. Mrs. Browning. [ 1913 Webster ]

2. (Crystallog.) Same as Tetragonal. [ 1913 Webster ]

Pyramidal numbers (Math.), certain series of figurate numbers expressing the number of balls or points that may be arranged in the form of pyramids. Thus 1, 4, 10, 20, 35, etc., are triangular pyramidal numbers; and 1, 5, 14, 30, 55, etc., are square pyramidal numbers. [ 1913 Webster ]

adv. Like a pyramid. [ 1913 Webster ]

{ } a. Of or pertaining to a pyramid; having the form of a pyramid; pyramidal. “ A pyramidical rock.” Goldsmith. “Gold in pyramidic plenty piled.” Shenstone. -- Pyr`a*mid"ic*al*ly, adv. Pyr`a*mild"ic*al*ness, n. [ 1913 Webster ]

‖n.; pl. Pyramidia [ NL., from L. pyramis. See Pyramid. ] The small pyramid which crowns or completes an obelisk. [ 1913 Webster ]

n. [ Gr. &unr_;, &unr_;, pyramid + -id: cf. F. pyramidoïde. ] A solid resembling a pyramid; -- called also pyramoid. Barlow. [ 1913 Webster ]

‖n.; pl. Pyramides [ L. ] A pyramid. [ 1913 Webster ]