Phonemes smallest speech units in language that can be distinguished perceptually. Different languages use different groups of about 20-80 phonemes (english has 40) Morphemes smallest units of meaning in a language. Include root word, prefixes and suffixes (e. g. unfriendly has all three) Semantics area of language concerned with understanding meaning of words and word combinations. Can include denotations (dictionary definition) and connotations (emotional overtones and secondary implications) Syntax system of rules that specify how words can be arranged into sentences. Sentence must have both subject and verb. Fast-mapping process by which children map a word onto an underlying concept after only one exposure. Overextension when child incorrectly uses word to describe wider set of objects/ actions than it is meant to. Ex) child might use the word ball for anything round orange, apple, moon. Underextensions when child incorrectly uses word to describe narrower set of objects/ actions than it is meant to.