(1):

(n.) The more or less cuplike calicle of a coral.

(2):

(n.) A sheath; a case; as, the theca, or cell, of an anther; the theca, or spore case, of a fungus; the theca of the spinal cord.

(3):

(n.) The chitinous cup which protects the hydranths of certain hydroids.

(4):

(n.) The wall forming a calicle of a coral.