Acid amide, a neutral compound formed by the substitution of the amido group for hydroxyl in an acid. [ 1913 Webster ]

Amido acid, an acid in which a portion of the nonacid hydrogen has been replaced by the amido group. The amido acids are both basic and acid. --
Amido group, amidogen, NH2. [ 1913 Webster ]

But rather famish them amid their plenty. Shak. [ 1913 Webster ]

Syn. -- Amidst, Among. These words differ to some extent from each other, as will be seen from their etymology. Amidst denotes in the midst or middle of, and hence surrounded by; as, this work was written amidst many interruptions. Among denotes a mingling or intermixing with distinct or separable objects; as, “He fell among thieves.” “Blessed art thou among women.” Hence, we say, among the moderns, among the ancients, among the thickest of trees, among these considerations, among the reasons I have to offer. Amid and amidst are commonly used when the idea of separate or distinguishable objects is not prominent. Hence, we say, they kept on amidst the storm, amidst the gloom, he was sinking amidst the waves, he persevered amidst many difficulties; in none of which cases could among be used. In like manner, Milton speaks of Abdiel, -- The seraph Abdiel, faithful found;
Among the faithless faithful only he, [ 1913 Webster ] because he was then considered as one of the angels. But when the poet adds, -- From amidst them forth he passed, [ 1913 Webster ] we have rather the idea of the angels as a collective body. Those squalid cabins and uncleared woods amidst which he was born. Macaulay. [ 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 ]

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 ]