Phoneme The individual distinguishable sound items in a language whose concatenation, in a particular order, produces morphemes. Phonemes are discrete, not continuously variable. Phonological or Phonemic identity is the sameness of the sound from the linguistic point of view.
Morpheme The smallest meaningful unit of a word, which in combination with other morphemes creates a word (in sign language, a visuomotor sign)
Phonetics The study of raw sounds. Phonetic identity, i.e., accoustic sameness: sounds may differ from speaker to speaker and generally from one utterance-event to the next.
Phonology The study of how sounds are used within a language - the permissible combinations of sounds
Morphology The study of words and word formation
Syntax The study of word order and sentence structure (in popular usage, ``grammar'')
Lexicon The collection of all words in a given language; each entry includes all information with morphological and syntactic ramification (but does not include conceptual knowledge?). The concept of a lexicon is theory-dependent.
Semantics The study of meaning (corresponding to all lexical items and to all possible sentences)
Prosody The vocal intonation that can modify the literal meaning of words and sentences
Pragmatics The study of language use
Discourse The linking of sentences such that they constitute a narrative