Lardil, also spelled Leerdil or Leertil, is a moribund language spoken by the Lardil people on Mornington Island (Kunhanha), in the Wellesley Islands of Queensland in northern Australia. Lardil is unusual among Aboriginal Australian languages in that it features a ceremonial register, called Damin (also Demiin). Damin is regarded by Lardil-speakers as a separate language and has the only phonological system outside Africa to use click consonants.

Lardil is a member of the Tangkic family of Non-Pama–Nyungan Australian languages, along with Kayardild and Yukulta, which are close enough to be mutually intelligible. Though Lardil is not mutually intelligible with either of these, it is likely that many Lardil speakers were historically bilingual in Yangkaal (a close relative of Kayardild), since the Lardil people have long been in contact with the neighboring Yangkaal tribe and trading, marriage and conflict between them seem to have been common. There was also limited contact with mainland tribes including the Yanyuwa, of Borroloola; and the Garawa and Wanyi, which groups ranged as far east as Burketown. Members of the Kaiadilt tribe (i.e. speakers of Kayardild) also settled on nearby Bentinck Island in 1947.

The number of Lardil speakers has diminished dramatically since Kenneth Hale's study of the language in the late 1960s. Hale worked with a few dozen speakers of Lardil, some of these fluent older speakers, and others younger members of the community who had only a working or passive understanding. When Norvin Richards, a student of Hale's, returned to Mornington Island to continue work on Lardil in the 1990s, he found Lardil children had no understanding of the language and that only a handful of aging speakers remained; Richards has stated that "Lardil was deliberately destroyed" by assimilation and relocation programs in the years of the "Stolen Generation". A dictionary and grammatical sketch of the language were compiled and published by the Mornington Shire Council in 1997, and the Mornington Island State School has implemented a government-funded cultural education program incorporating the Lardil language. The last fluent speaker of so-called Old Lardil died in 2007, though a few speakers of a grammatically distinct New variety remain.

While very few speakers of Lardil in its traditional form remain, Norvin Richards and Kenneth Hale both worked with some speakers of a "New Lardil" in the 1990s which displays significant morphological attrition compared to the Old variety. Previously minor sentence forms in which the object of a verb takes nominative case have become generalized, even in instances where the verb is in future tense (objects of future verbs historically inflected for futurity). One of a number of negation patterns has become generalized, and the augmented forms of monosyllabic verb roots reinterpreted as base forms.

Traditionally, the Lardil community held two initiation ceremonies for young men. Luruku, which involved circumcision, was undergone by all men following the appearance of facial hair; warama, the second initiation, was purely voluntary and culminated in a subincision ceremony.

Luruku initiates took a year-long oath of silence and were taught a sign language known as marlda kangka (literally, 'hand language'), which, though limited in its semantic scope, was fairly complex. Anthropologist David McKnight's research in the 1990s suggests that marlda kangka classifies animals somewhat differently from Lardil, having, for example, a class containing all shellfish (which Lardil lacks) and lacking an inclusive sign for 'dugong+turtle' (Lardil dilmirrur). In addition to its use by luruku initiates, marlda kangka had practical applications in hunting and warfare.

While marlda kangka was essentially a male language, the non-initiated were not forbidden to speak it. Damin, on the other hand, was (at least nominally) a secret language spoken only by warama initiates and those preparing for second initiation, though many community members seem to have understood it. Damin, like marlda kangka, was phonologically, lexically and semantically distinct from Lardil, though its syntax and morphology seem to be analogous. Research into the language has proved controversial, since the Lardil community regards it as cultural property and no explicit permission was given to make Damin words public.

The consonant inventory is as follows, with the practical orthography in parentheses.