Words grow by attaching smaller pieces. An affix is a bound morpheme fixed to a root or stem to change meaning or grammatical function.

Prefixes go before the root, suffixes after it, infixes inside it, and circumfixes around it. English leans on prefixes and suffixes; other languages make heavier use of infixes or templatic morphology. Affixes may derive new words or inflect existing ones for tense, number, or case.

Recognizing affixes helps readers parse unfamiliar vocabulary. Historical linguists watch affixes erode, fuse, or arise from independent words. The set of productive affixes shapes how freely a language coins new terms.

• Bound morpheme attached to a base
• Includes prefixes, suffixes, infixes, circumfixes
• May be derivational or inflectional
• Central to word formation