Top Definition
a male human with a small penis who is completely unaware or unable to accept his diminuitive size and believes he can "conquer the universe" of women
Susan: I slept with Peter last night.

Friend: Oh yeah, how was he? He seems like THE MAN about town. Does he have big one?

Susan: OMG! No, he is such a micronaut. You wouldn't even know based on how he thinks he can get women.
by freshfields April 01, 2010
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