1.nounA tiny freshwater fish, Poecilia reticulata, popular in home aquariums, that usually has a plain body and black or dark blue tail for the females and a more colorful tail for the males.
"Fred kept a tank of guppies by the windowsill."
2.nounBy extension, any tiny fish.
3.nounA tube holding paintballs before they are loaded into the gun.
"2001, John R. Little, Curtis Wong, Ultimate Paintball Field Guide (page 177)"