Munsee (also known as Munsee Delaware, Delaware, Ontario Delaware, Delaware: Huluníixsuwaakan, Monsii èlixsuwakàn) is an endangered language of the Eastern Algonquian subgroup of the Algonquian language family, itself a branch of the Algic language family. Munsee is one of two Delaware languages (also known as Lenape languages, after the tribe's autonym). It is very closely related to the Unami Delaware, but the two are sufficiently different that they are considered separate languages. Munsee was spoken aboriginally by Lenape in the vicinity of the modern New York City area in the United States, including western Long Island, Manhattan Island, Staten Island, as well as adjacent areas on the mainland: southeastern New York State, the northern third of New Jersey, and northeastern Pennsylvania.

As of 2018, Munsee was spoken only on the Moraviantown Reserve in Ontario, Canada, by two elderly individuals, aged 77 and 90, making it critically endangered. As of 2022, only one elderly native speaker remained. When the number of speakers was somewhat larger, the language was reported to differ between individual speakers, each having a personal dialect. There has been interest in learning the language by younger individuals. Some researchers and universities have partnered with indigenous communities in an effort to revitalize the language, notably Montclair State University and the University of Toronto.

Munsee is an Eastern Algonquian language, which is the sole recognized genetic subgroup descending from Proto-Algonquian, the common ancestor language of the Algonquian language family. Munsee is very closely related to Unami Delaware. Munsee and Unami constitute the Delaware languages, comprising a subgroup within Eastern Algonquian. Taken together with Mahican, the Delaware languages constitute Delawaran, a subgroup within Eastern Algonquian.

The term Munsee developed as an English name for the aggregated group that formed along the upper Delaware River north of the Delaware Water Gap. Other Munsee dialect speakers joined the Minisink group; the earliest recorded mention of Munsee dates from 1725. Minisink is a Munsee term meaning 'at the island', and is to be transcribed mə̆nə́sənk. It is the locative form of a now disused word /mənə́s/ 'island' (no source given, not a form given in records and not a normal Munsee noun ending; viz. manan, manhan; form suggests 'small island'); cognates in other Algonquian languages are e.g. Ojibwe minis, 'island'. Orthographic ⟨ink⟩ in the form Minisink is the modern Munsee locative suffix /-ənk/ (discussed below in the section "Grammar"). The term Munsee is the English adaptation of a regularly formed word, mə́n'si·w 'person from Minisink'.

Over time the British extended the term Munsee to any speaker of the Munsee language. Attempts to derive Munsee from a word meaning 'stone' or 'mountain', as proposed by Brinton, are incorrect. Kraft's claim that Munsee is not an indigenous term, and that it results from a "corruption" of English use of Minisink is incorrect. The term follows a regular pattern of Munsee word formation.

Names for the speakers of Munsee are used in complex ways in both English and in Munsee. The Unami language is sometimes treated as "Delaware" or "Delaware proper", reflecting the original application of the term Delaware to Unami speakers, but Munsee speakers use Delaware as a self-designation in English. The term Delaware was originally applied by British colonists to Unami speakers living along the Delaware River, which is named after Lord De La Warr, the first governor of Virginia. The term was gradually extended to refer to all Delaware groups.

The Munsee in Ontario are sometimes referred to as "Ontario Delaware" or "Canadian Delaware". Munsee-speaking residents of Moraviantown use the English term Munsee to refer to residents of Munceytown, approximately 50 km (31 mi) to the east. In English, Moraviantown residents call themselves Delaware, and in Munsee /lənáːpeːw/ 'Delaware person, Indian'.

Some Delaware at Moraviantown also use the term Christian Indian as a preferred self-designation in English. The equivalent Munsee term is ké·ntə̆we·s 'one who prays, Moravian convert'. Munsee speakers refer to Oklahoma Delaware as Unami in English or /wə̆ná·mi·w/ in Munsee. The English term Lenape is of Unami origin, and is used in English as a self-designation by speakers of Unami;