Definition of mayfly
: any of an order (Ephemeroptera) of insects with an aquatic nymph and a short-lived, fragile adult lacking mouthparts and having membranous, heavily veined wings and two or three long, threadlike tails ◆the wings of the mayfly are held vertically above the body when closed. —called also ephemerid
MAYFLY Defined for English Language Learners
Definition of mayfly for English Language Learners
: a small flying insect that lives for only a short time
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