idioblast

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A plant cell that differs noticeably in form from neighboring cells.

Century Dictionary and Cyclopedia

1. n. A term proposed by Sachs for certain individual cells or tissue-elements which differ greatly, as regards their contents, from the surrounding tissues. Such are the resin-cells, tannin-cells, crystal-cells, etc., found in various plants.
2. n. In biology, one of the hypothetical, ultimate elements of living protoplasm, similar to the gemmules of Darwin, the physiological units of Herbert Spencer, the biophores of Weismann, etc.

Wiktionary

1. n. botany An isolated specialised cell found in the midst of an otherwise homogeneous group of cells in plant tissue.

GNU Webster's 1913

1. n. (Bot.) An individual cell, differing greatly from its neighbours in regard to size, structure, or contents.