Merriam-Webster's Collegiate® Dictionary, 11th Edition
TAXI
I. noun (plural taxis; also taxies)
Date: circa 1907
taxicab ,
II. verb (taxied; taxiing; taxis or taxies)
Date: 1911
intransitive verb
1. to go at low speed along the surface of the ground or water, to operate an aircraft on the ground under its own power, to ride in a taxicab , transitive verb to transport by or as if by taxi, to cause (an aircraft) to taxi