In linguistics, a marker is a free or bound morpheme that indicates the grammatical function of the marked word or sentence. In analytic languages and agglutinative languages, markers are generally easily distinguished. In fusional languages and polysynthetic languages, this is often not the case. In the Latin word amo, "I love", for instance, the suffix -o marks indicative mood, active voice, first person, singular, present tense. Latin is a highly fusional language.

A lexeme is called marked if it contains a marker, and unmarked if not. In nominative-accusative languages, the nominative case is typically unmarked.

Examples

• English: the suffix -s in dogs is a plural marker
• Latin: the suffix -is in flaminis is a case marker, specifically a genitive marker
• Spanish: the word hay in hay muchos libros en la biblioteca is an existential marker
• Japanese: the Japanese particle が (ga) in ジョンが学生です。[Jon ga gakusei desu.] 'John is a student.' is a subject marker