An agglutinative language is a type of synthetic language with morphology that primarily uses agglutination: words may contain different morphemes to determine their meaning, but each of these morphemes (including stems and affixes) remains in every aspect unchanged after their union, thus resulting in generally easier deducible word meanings if compared to fusional languages, which allow modifications in either or both the phonetics or spelling of one or more morphemes within a word, generally for shortening the word on behalf of an easier pronunciation. Agglutinative languages have generally one grammatical category per affix while fusional languages have multiple. The term was introduced by Wilhelm von Humboldt to classify languages from a morphological point of view. It is derived from the Latin verb agglutinare, which means "to glue together".
Non-agglutinative synthetic languages are fusional languages; morphologically, they combine affixes by "squeezing" them together, drastically changing them in the process, and joining several meanings in a single affix (for example, in the Spanish word comí "I ate", the suffix -í carries the meanings of first person, singular number, past tense, indicative mode, active voice.) The term agglutinative is sometimes incorrectly used as a synonym for synthetic. Used in this way, the term embraces both fusional languages and inflected languages. The agglutinative and fusional languages are two ends of a continuum, with various languages falling more toward one or the other end. For example, Japanese is generally agglutinative, but displays fusion in otōto (?), from oto+hito (originally woto+pito), and in its non-affixing verb conjugations. A synthetic language may use morphological agglutination combined with partial usage of fusional features, for example in its case system (e.g., younger brotherGerman, Dutch, and Persian).