In linguistics, a cognate object (or cognate accusative) is a verb's object that is etymologically related to the verb. More specifically, the verb is one that is ordinarily intransitive (lacking any object), and the cognate object is simply the verb's noun form. For example, in the sentence He slept a troubled sleep, sleep is the cognate object of the verb slept. Cognate objects exist in many languages, including various unrelated ones; for example, they exist in Arabic, Chichewa, German, Ancient Greek, Hebrew, Icelandic, Korean, Latin, and Russian.
In English, the construction can occur with a number of intransitive verbs, which then become transitive:
- He slept a troubled sleep. (He slept, and his sleep was troubled.)
- He laughed a bitter laugh. (He laughed bitterly.)
- He dreamed a strange dream. (He dreamed, and his dream was strange.)
(That seems to be the only example that has a more natural-sounding sentence that would be used in everyday conversation: "He had a strange dream.")
- He walked their walk and talked their talk. (He walked and talked as they did.)
- He smiled a charming smile. (He smiled, and his smile was charming.)
- He danced a cheerful dance. (He danced, and his dance was cheerful.)
- He died a painful death. (He died painfully.)
In some of these cases, the cognate object allows for a simpler construction. In others, it may be chosen for idiomatic or rhetorical reasons. In general, the cognate object's modifiers are in some sense modifying the verb: for example, He slept a troubled sleep tells how he slept. Semantically, many of these verbs denote modes of nonverbal expression (laugh, smile) and bodily actions or motions (dance, walk, sleep), specifically including what Levin calls "waltz verbs," those that are zero-related (identical) to the names of dances. 
- Pleonasm (the use of more words than necessary to express an idea)
- Polyptoton (a stylistic scheme in which words derived from the same root are repeated)
- Linguist list
- Herbert Weir Smyth. A Greek grammar for colleges. page 355, section 1563: cognate accusative
- Joseph Henry Allen, James Bradstreet Greenough. New Latin grammar for schools and colleges. p. 243, section 390: cognate accusative.
- Levin, Beth. English Verb Classes and Alternations: A Preliminary Investigation. Chicago and London: The University of Chicago Press. pp. 95–6.