(geometry) A four-dimensional polytope whose twenty-four bounding facets are octahedra and which has no three-dimensional analogue.

(geometry) A four-dimensional polytope, analogous to an octahedron, whose sixteen bounding facets are tetrahedra.

(geometry) A four-dimensional polytope, analogous to a dodecahedron, whose 120 bounding facets are dodecahedra.

(geometry) A four-dimensional polytope, analogous to an icosahedron, whose 600 bounding facets are tetrahedra.

(geometry) A four-dimensional polytope, analogous to a tetrahedron, whose five bounding facets are tetrahedra.

(geometry) A four-dimensional polytope, analogous to a cube, whose eight bounding facets are cubes; a tesseract.

(physics) A very small galvanic cell formed by differences in potential between adjacent areas of a metal surface in contact with an electrolyte; implicated in surface corrosion

colloblast

One of the long, slender, conducting cells of the phloem that do not form a constituent element of a sieve tube, but which are provided with relatively unspecialized sieve areas, especially in the tapering ends of the cells that overlap those of other sieve cells. Sieve cells are typically associated with gymnosperms.

A kind of specialized cell located in the lower leaf epidermis of plants. Pairs of guard cells surround tiny stomatal airway pores and regulate their opening and closing.