tadpole

WordReference Random House Learner's Dictionary of American English © 2019

tad•pole /ˈtædpoʊl/   n. [countable]

1. Reptiles the larva of frogs and toads, living in water, having internal gills and a tail.

WordReference Random House Unabridged Dictionary of American English © 2019

tad•pole  (tad′pōl), n. 

1. Reptiles the aquatic larva or immature form of frogs and toads, esp. after the development of the internal gills and before the appearance of the forelimbs and the resorption of the tail.

• late Middle English tad(de)pol, equivalent. to tad(de) toad + pol poll¹ (head) 1400–50

Collins Concise English Dictionary © HarperCollins Publishers::

tadpole /ˈtædˌpəʊl/ n

1. the aquatic larva of frogs, toads, etc, which develops from a limbless tailed form with external gills into a form with internal gills, limbs, and a reduced tail

Etymology: 15th Century taddepol, from tadde toad + pol head, poll