Tadpole \Tad"pole`\, n. [OE. tadde toad (AS. t[=a]die, t[=a]dige) + poll; properly, a toad that is or seems all head. See Toad, and Poll.]

1. (Zo["o]l.) The young aquatic larva of any amphibian. In this stage it breathes by means of external or internal gills, is at first destitute of legs, and has a finlike tail. Called also polliwig, polliwog, porwiggle, or purwiggy.

2. (Zo["o]l.) The hooded merganser. [Local, U. S.]

Tadpole fish. (Zo["o]l.) See Forkbeard
   (a) .

Source: Webster's Revised Unabridged Dictionary (1913)