hemlock, any tree of the genus Tsuga, coniferous evergreens of the family Pinaceae (pine family) native to North America and Asia. The common hemlock of E North America is T. canadensis, an ornamental tree (sometimes cultivated as a hedge) with small cones and short, dark green leaves so arranged as to give the branchlets a flattened appearance. The tree has been highly valued as a source of tanbark but is now seriously reduced in number. Its wood is soft and light. One of the two Western hemlocks (T. heterophylla, the tallest tree of the genus) has more valuable wood, which is used in construction work. The ground hemlock is a species of yew. The poison hemlock and water hemlock are herbs of the family Umbelliferae (carrot family) of the division Magnoliophyta. True hemlock is classified in the division Pinophyta, class Pinopsida, order Coniferales, family Pinaceae.

Any of several poisonous herbaceous plants of the parsley family, especially Conium maculatum, believed to be the plant that killed Socrates. It is now common in the U.S. as well as in Europe. A tall biennial, this plant has green stems spotted with red or purple, large compound leaves, and white flowers. Though the poison is concentrated in the seeds, the entire plant is dangerous to livestock when fresh. Despite their common name, poison hemlocks are not conifers (see hemlock). Water hemlocks (Cicuta species) are similar and also dangerous.

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Any of 10 species of coniferous evergreen trees that make up the genus Tsuga, in the pine family, native to North America and central and eastern Asia. Some are important timber trees, and many are popular ornamentals. Other plants commonly called hemlock include ground hemlock (see yew) and poison hemlock and water hemlock (parsley family). A true hemlock is a tall, pyramidal tree with purplish or reddish-brown bark, slender horizontal or drooping branches, and short, blunt leaves that grow from woody cushionlike structures on the twigs.

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The word hemlock may refer to:

• Conium, or more specifically, Conium maculatum, a common European herb that contains the alkaloid coniine and was probably the state poison of Ancient Greece, and the purported poison used in the execution of Socrates.
• Several other poisonous plants in the family Apiaceae (formerly Umbelliferae) are sometimes called hemlock:
• Water Hemlock or cowbane
• Hemlock Water Dropwort (Oenanthe crocota) is a species in the related genus Oenanthe

• Tsuga, a genus of conifers originally named "hemlocks" due to a perceived similarity in the scent of the crushed foliage to that of Conium.

Localities

• Hemlock Falls, Georgia
• Hemlock, Indiana
• Hemlock, Michigan
• Hemlock, New York
• Hemlock, Ohio
• Hemlock, Ontario
• Hemlock Township, Pennsylvania

Other uses

• Hemlock Society, a group advocating assisted suicide
• Hemlock (company), a chemicals manufacturer specializing in silicon products
• Hemlock, a variant of the Emacs text editor for Unix
• Hemlock Records, a record label based out of Chicago, Illinois
• Hemlock is a heavy metal band from Las Vegas, Nevada
• Hemlock is a 1990s punk band from San Diego, California
• Hemlock was also the name of a black metal project by bass player Dan Lilker
• Sherlock Hemlock, the name of a Muppet detective
• Hemlock (play), an original play by playwright Bob Jude Ferrante
• Hemlock's Diary is a political, economic and social blog written in Hong Kong
• Hemlock, an Iranian movie also released as Shokaran and starring Hediyeh Tehrani
• Hemlock, a fictional Russian assassin in JAG