STOMA

n. mouth or mouthlike opening (Zoology); microscopic opening, pore (Botany)

In botany, a "stoma" (also stomate; plural stomata) is a tiny opening or pore, found mostly on the underside of a plant leaf, and used for gas exchange. The pore is formed by a pair of specialized sclerenchyma cells known as guard cells which are responsible for regulating the size of the opening. Air containing carbon dioxide enters the plant through these openings where it gets used in photosynthesis and respiration.  Oxygen produced by photosynthesis in the parenchyma cells (parenchyma cells with pectin) of the leaf interior exits through these same openings. Also, water vapor is released into the atmosphere through these pores in a process called transpiration.
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Stoma /sto·ma/ pl. sto´mas, sto´mata [Gr.] a mouthlike opening, particularly an incised opening which is kept open for drainage or other purposes. [more]Stoma - Community and Resources

Noun
1. a minute epidermal pore in a leaf or stem through which gases and water vapor can pass
(synonym) stomate, pore
(hypernym) aperture
(hyponym) hydathode, water pore, water stoma
2. a mouth or mouthlike opening (especially one created by surgery on the surface of the body to create an opening to an internal organ)
(hypernym) orifice, opening, porta
(part-holonym) colostomy
(classification) surgery

n. stoma, mouth or mouthlike opening