poison oak

American  

noun

1. either of two shrubs, Rhus toxicodendron, of the eastern United States, or R. diversiloba, of the Pacific coast of North America, resembling poison ivy and causing severe dermatitis when touched by persons sensitive to them.

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poison oak British  

noun

1. either of two North American anacardiaceous shrubs, Rhus toxicodendron or R. diversiloba, that are related to the poison ivy and cause a similar rash See also sumach

2. (not in technical use) another name for poison ivy

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Etymology

Origin of poison oak

An Americanism dating back to 1735–45

Example Sentences

Rangers describe the trail — a steep half-mile to reach the cave, then a half-mile loop inside — as “strenuous,” featuring possible encounters with poison oak, bees, rattlesnakes and falling rocks.

From Los Angeles Times • Apr. 7, 2025

Its sparse plant life consists of scraggly shrubs and pines, along with thickets of poison oak.

From New York Times • Dec. 24, 2023

BY COMPARISON, “the fox war” seems rather like fighting to protect dandelions and poison oak in a rare-plant garden.

From Seattle Times • Aug. 4, 2023

There are several ways to look out for poison oak, starting with the old adage, “Leaves of three let it be,” Trimble said.

From Los Angeles Times • May 24, 2023

He talks about the plans for the house: the skylights, expanding the deck, planting flower beds of tulips and crocuses, clearing the poison oak, adding another wing, building a Japanese-style tile bathroom.

From "The Joy Luck Club" by Amy Tan