Definition of "superfetation" [su•per•fe•ta•tion]

• Formation or development of a second fetus when one is already present in the uterus, occurring normally in some animal species. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "There have been only 10 recorded cases of the phenomenon, dubbed superfetation."
• "It's called "superfetation," and I guess it happens... not only can you get pregnant while on your period, etc., I guess you can get pregnant ANYTIME."
• "She addressed the controller of excise as “M. Chatelet,” and left that gentleman thunderstruck by the discovery that she knew about the illegal superfetation of the particle."