The American Heritage® Dictionary of the English Language, 4th Edition
n. See macrogamete.
The Century Dictionary and Cyclopedia
n. A large gamete or germ-cell, as distinguished from a microgamete; a macrogamete. The ovum is a megagamete, the spermatozoon a microgamete; the two unite to form a zygote.
Word Usage
"In previous discussions of the subject I have urged that the only meaning of sex was the difference between the megagamete or ovum, and the microgamete or sperm."