Dictionary.com
Thesaurus.com

gamete vs. zygote

[gam-eet, guh-meet] / ˈgæm it, gəˈmit /

noun

Biology.
  1. a mature sexual reproductive cell, as a sperm or egg, that unites with another cell to form a new organism.

[zahy-goht, zig-oht] / ˈzaɪ goʊt, ˈzɪg oʊt /

noun

Biology.
  1. the cell produced by the union of two gametes, before it undergoes cleavage.