isogamete

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A gamete that has the same size and structure as the one with which it unites.

from The Century Dictionary.

• noun One of two equal cells that unite to form a zygote.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biology Either of a pair of conjugating gametes that are of the same size and structure

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun either of a pair of conjugating gametes of the same size and structure