Morphological derivation, in linguistics, is the process of forming a new word from an existing word, often by adding a prefix or suffix, such as un- or -ness. For example, unhappy and happiness derive from the root word happy.
It is differentiated from inflection, which is the modification of a word to form different grammatical categories without changing its core meaning: determines, determining, and determined are from the root determine.
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A valediction (derivation from Latin vale dicere 'to say farewell'), parting phrase, or complimentary close in American English, is an expression used to say farewell, especially a word or phrase used to end a letter or message, or a speech made at a farewell.
Valediction's counterpart is a greeting called a salutation.
In linguistics, reduplication is a morphological process in which the root or stem of a word, part of that, or the whole word is repeated exactly or with a slight change.
The classic observation on the semantics of reduplication is Edward Sapir's: "Generally employed, with self-evident symbolism, to indicate such concepts as distribution, plurality, repetition, customary activity, increase of size, added intensity, continuance." It is used in inflections to convey a grammatical function, such as plurality or intensification, and in lexical derivation to create new words. It is often used when a speaker adopts a tone more expressive or figurative than ordinary speech and is also often, but not exclusively, iconic in meaning. It is found in a wide range of languages and language groups, though its level of linguistic productivity varies. Examples can be found in language as old as Sumerian, where it was used in forming some color terms, e.g. babbar "white", kukku "black".
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). 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.
In linguistics, an agent noun (in Latin, nomen agentis) is a word that is derived from another word denoting an action, and that identifies an entity that does that action. For example, driver is an agent noun formed from the verb drive.
Usually, derived in the above definition has the strict sense attached to it in morphology, that is the derivation takes as an input a lexeme (an abstract unit of morphological analysis) and produces a new lexeme. However, the classification of morphemes into derivational morphemes (see word formation) and inflectional ones is not generally a straightforward theoretical question, and different authors can make different decisions as to the general theoretical principles of the classification as well as to the actual classification of morphemes presented in a grammar of some language (for example, of the agent noun-forming morpheme).