Words and their parts

Carstairs-McCarthy (2004)
Morphology – study of morphemes
Morpheme – minimal meaningful unit

Carstairs-McCarthy (2004: 141)
Allomorph – a variant pronunciation of a morpheme; the choice is determined by context (phonological, grammatical, or lexical)

Carstairs-McCarthy (2004: 144–145)
Monomorphemic – consisting of only one morpheme
cat
Polymorphemic – consisting of more than one morpheme
cats
disorganized

allomorphy
illegible
irresponsible
implausible, immature
inexperienced

free morpheme, free allomorph – one that occurs independently as a word
Bound morpheme, bound allomorph – one that does not occur independently as a word

asleep
sleep – free morpheme
a- – bound morpheme

Carstairs-McCarthy (2004: 143)
A morpheme may have both free and bound allomorphs, e.g.
wife – free allomorph
Wives – wive- bound allomorph

Carstairs-McCarthy (2004: 142)
Cranberry morph(eme) – morpheme (or allomorph) that occurs in only one word (more precisely, only one lexeme)
cranberry

Carstairs-McCarthy (2004: 144)
root – the morpheme that makes the most precise and concrete contribution to the word’s meaning and is either the sole morpheme or else the only one that is not a prefix or a suffix. In English, especially in its inherited Germanic vocabulary; most roots are free; e.g.
cat
unhelpful (help)
Visible, vision (vis-)

Carstairs-McCarthy (2004: 141)
base – word or part of a word that is viewed as an input to a derivational or inflectional process, in particular affixation