Grammaticalization

Grammaticalization is a diachronic process by which grammatical items arise from constructions with lexical items.

Example
The Romance synthetic future (e.g. Spanish cantará 'will sing') was grammaticalized from a periphrastic construction consisiting of infinitive + 'have' (Latin cantare habet > cantar ha > cantará).

Synonyms

 * grammaticization (used especially by Joan Bybee and her colleagues)
 * agglutination (this term was used for grammaticalization in the 19th century)

Quotations

 * "Grammaticalization consists in the increase of the range of a morpheme advancing from a lexical to a grammatical or from a less grammatical to a more grammatical status, e.g. from a derivative formant to an inflectional one." (Kurylowicz 1965 [1975]: 52)

Origins
The term was apparently first used by Meillet (1912).