Definition · Plain-language
Affix
An affix is a meaningful word part added to a root to change its meaning or grammar — the umbrella term covering prefixes, suffixes and infixes.
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The umbrella term for word parts
An affix is any element attached to a root or base word to modify its meaning or grammatical role. As a category, affix covers the more familiar prefix and suffix, plus the rarer infix and circumfix. All affixes are bound morphemes — they cannot stand alone as words but only exist attached to something else. In unhelpfulness, the root help carries two affixes: the prefix un- before it and the suffixes -ful and -ness after. The process of adding affixes, called affixation or derivation, is among the most productive mechanisms by which English and many other languages create new vocabulary.
Types of affix by position
Affixes are named according to where they attach. A prefix goes at the start (re-, un-, pre-), usually changing meaning. A suffix goes at the end (-ness, -able, -ed), often changing the part of speech as well. An infix is inserted inside a root; English has almost none, the nearest being expletive insertions in informal speech (abso-blooming-lutely). A circumfix wraps around a root in two parts at once, common in some languages but not in standard English. By function, affixes are also split into derivational (forming new words) and inflectional (marking grammar such as tense or plural).
Affix, morpheme and root
These terms nest together. A morpheme is any smallest unit of meaning; a root is the morpheme carrying core meaning; and an affix is a bound morpheme added to a root. So affixes are a sub-set of morphemes, defined by being bound and by attaching to a base. Understanding affixes is a powerful vocabulary tool: recognising that un- negates, that -less means without, and that -tion forms a noun lets a reader decode unfamiliar words by parts. Spelling sometimes changes at the join — happy plus -ness becomes happiness — because affixes interact with the letters and sounds of the root they meet.
Key facts
At a glance
- Definition: a word part added to a root to change meaning or grammar
- Umbrella for: prefixes, suffixes, infixes and circumfixes
- Nature: always a bound morpheme (cannot stand alone)
- By position: prefix (before), suffix (after), infix (inside)
- By function: derivational (new words) or inflectional (grammar)
- Example: un- + help + -ful + -ness → unhelpfulness
Common misconceptions
What people often get wrong
Often heard: Affix is just another word for suffix.
Actually: Affix is the umbrella term. A suffix is one kind of affix (added at the end); prefixes (added at the start) and infixes (added inside) are affixes too. Affix covers them all.
Often heard: An affix can be used as a word on its own.
Actually: Affixes are bound morphemes and never stand alone. Un-, -ness and re- only carry meaning when attached to a root or base word.
Often heard: English uses infixes as commonly as prefixes and suffixes.
Actually: English relies heavily on prefixes and suffixes but has almost no true infixes — the nearest are informal expletive insertions. Infixes are far more common in some other languages.
Going deeper
