Relationship between two people who share no common genetic material but who share eerily similar mannerisms, speech patterns, behaviors and/or appearance
"Are you two brother and sister??"
"What? No! We are not at allrelated "
"Well you're definitely non-zygotic twins then , because you act so much alike it is freaky"
Zygote is a way to refer to very young people. Since the "real" definition of a zygote is sperm + egg; zygote is a slang version of referring to a very young person.
Often it is a more extreme version of the term "fetus," which is also used to describe young people.
Polite but meaningful phrase to convey that the couple are trying to conceive a child, particularly if the parents are crazy in love. A riff on "psychotic episode"
An insult pertaining to an individual who has failed to develop further than a zygote, coined by grump of Game Grumps Arin Hanson (The video game boy, the one who wins)