noun a stigma. ·see stigma, ·noun, 6 (a) & (b).
2. stoma ·noun one of the minute apertures between the cells in many serous membranes.
3. stoma ·noun the minute breathing pores of leaves or other organs opening into the intercellular spaces, and usually bordered by two contractile cells.
4. stoma ·noun the line of dehiscence of the sporangium of a fern. it is usually marked by two transversely elongated cells. ·see ·illust. of sporangium.