Definition of hairstreak
: any of a subfamily (Theclinae of the family Lycaenidae) of small butterflies usually having striped markings on the underside of the wings and thin filamentous projections from the hind wings
First Known Use of hairstreak
Learn More about hairstreak
Britannica.com: Encyclopedia article about hairstreak
Seen and Heard
What made you want to look up hairstreak? Please tell us where you read or heard it (including the quote, if possible).