Word-formation is the brunch of lexicology which studies the derivative structure of existing words and the patterns on which a language builds new words.
Word-formation is the system of derivative types of words and the process of creating new words from the material available in the language after certain structural and semantic formulae and patterns.
There are different classes according to different principles: morphological; syntactic; lexico-semantic.
There exist 4 main ways of word building in modern English: derivation affixation; composition; conversion; shortening abbreviation.
There are also secondary ways of word-building: sound interchange; stress interchange; sound imitation; blending; back formation; reduplication.
The conformity with structural types of words the following 2 types of word-formation distinguished: word-derivation; word-compounding.
Words created by word derivation have 1 derivational base and 1 derivational affixation. e.g.: overestimate.
Some derived words have no derivative affixes because derivation is achieved through conversion. e.g.: fall, n.; fall, v.
Word created by word composition have at least 2 bases. e.g.: ice-cold.
Word-formation may be studied from 2 angles: synchronically; diachronically.
Diachronically it is the chronological order of formation of 1 word from some other word that is relevant. Synchronically a derived word is regarded as having an even more complex structure that its correlated words regardless of the fact if it was derived from a synchro base or a more complex base.
