- The definition of their is a person or thing that belongs to or was made by them.
- An example of their is a sister of two siblings.
- An example of their is a book written by two authors.
Origin: Middle English theyr from Old Norse theirra, genitive plural of the demonstrative pronoun replacing Middle English here, Old English hira: see they
Used by arrangement with John Wiley & Sons, Inc.
adjective The possessive form of they.
- Used as a modifier before a noun: their accomplishments; their home town.
- Usage Problem His, her, or its: “It is fatal for anyone who writes to think of their sex” (Virginia Woolf). See Usage Notes at he1, they.
Origin: Middle English, from Old Norse theira, theirs; see to- in Indo-European roots.