Valonia

Part of speech: noun (n.)

1. The acorn cup of two kinds of oak (Quercus macrolepis, and Q. vallonea) found in Eastern Europe. It contains abundance of tannin, and is much used by tanners and dyers.

2. A genus of marine green algæ, in which the whole frond consists of a single oval or cylindrical cell, often an inch in length.