In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns and adjectives, and verb endings, which form the conjugation of verbs. Suffixes can carry grammatical information (inflectional endings) or lexical information (derivational/lexical suffixes).^[1] Inflection changes the grammatical properties of a word within its syntactic category. Derivational suffixes fall into two categories: class-changing derivation and class-maintaining derivation.

Particularly in the study of Semitic languages, suffixes are called affirmatives, as they can alter the form of the words. In Indo-European studies, a distinction is made between suffixes and endings (see Proto-Indo-European root).

A word-final segment that is somewhere between a free morpheme and a bound morpheme is known as a suffixoid^[2] or a semi-suffix^[3] (e.g., English -like or German -freundlich "friendly").

Inflection changes the grammatical properties of a word within its syntactic category. In several languages, this is realized by an inflectional suffix, also known as desinence. In the example:

I was hoping the cloth wouldn't fade, but it has faded quite a bit.

the suffix -d inflects the root-word fade to indicate past participle.

Inflectional suffixes do not change the word class of the word after the inflection.^[5] Inflectional suffixes in Modern English include:

Derivational suffixes can be divided into two categories: class-changing derivation and class-maintaining derivation.^[6] In English, they include

• -able/-ible (usually changes verbs into adjectives)
• -al /-ual (usually changes nouns into adjectives)
• -ant (usually changes verbs into nouns, often referring to a human agent)
• -ess (usually class-maintaining, with the word class remaining a noun)
• -ful (usually changes nouns into adjectives)
• -fy (usually changes nouns into verbs)
• -hood (usually class-maintaining, with the word class remaining a noun)
• -ise/-ize (usually changes nouns into verbs)
• -ish (usually changes nouns into adjectives/class-maintaining, with the word class remaining an adjective)
• -ism (usually class-maintaining, with the word class remaining a noun)
• -ist (usually class-maintaining, with the word class remaining a noun)
• -ity (usually changes adjectives into nouns)
• -less (usually changes nouns into adjectives)
• -like (usually changes nouns into adjectives)
• -logy/-ology (usually class-maintaining, with the word class remaining a noun)
• -ly (usually changes adjectives into adverbs, but also some nouns into adjectives)
• -ment (usually changes verbs into nouns)
• -ness (usually changes adjectives into nouns)
• -oid (usually changes nouns into adjectives)
• -tion/-ion/-ation (usually changes verbs into nouns)
• -um (usually) museum; stadium; auditorium; aquarium; planetarium; medium
• -wise From wīse ("manner, way, condition, direction")

A suffix will often change the stress or accent pattern of a multi-syllable word, altering the phoneme pattern of the root word even if the root's morphology does not change.^[7] An example is the difference between "photograph" and "photography". In this case, the "-y" ending governs the stress pattern, causing the primary stress to shift from the first syllable ("pho-") to the antepenultimate ("-to-"). The unaccented syllables have their ordinary vowel sound changed to a schwa. This can be a particular problem for dyslexics, affecting their phonemic awareness,^[8] as well as a hurdle for non-native speakers.