1. ROOT (BASE), STEM
Root: is the irreducible core of word, with absolutely nothing else attached to it (It has potential of being attached). It is a part that is always present, possibly with some modification, in the various manifestations of a lexeme. For example ‘walk’ becomes walks, walking, or walked.
‘good’ become better, or well.
Root can also be called as base (any unit whatsoever to which affixes of any kind can be added). The affixes can be inflectional or derivational.
Stem is that part of a word that is in existence before any inflectional affixes. (i.e. those affixes whose presence is required by the syntax such as markers of singular and plural number in nouns, tense in verbs etc.) For example:
‘workers’: work is a root, worker is a stem.
‘ cats’: cat is a stem (root).

2. MORPHEME, MORPH, AND ALLOMORPH
The morpheme is the smallest difference in the shape of a word that correlates with the smallest different in word of sentence meaning or in grammatical structure. A morph is a physical form representing some morpheme in a language. It is a recurrent distinctive sound (phoneme) or sequence of sounds (phonemes) Example: Morpheme Morph I /ai/ she /∫i:/ he /hi:/ car /ka:/ park /pa:k/ mend /mend/

3. MORPHEME, MORPH, ALLOMORPH (Cont….)
Allomorph is different morphs represent the same morpheme (The same morpheme that is represented by several morphs).
Example:
The morpheme -ed are represented by the following morphs:
a. /Id/ if the verb ends in /d/ or /t/
/mend/ - /mendId/, /peint/ - /peintId/
‘mend –mended’, ‘paint – painted’
b. /d/ after a verb ending in any voiced sound except /d/
/kli:n/ - /kli:nd/, /weI/ - /weId/
‘clean – cleaned’, ‘weigh – weighed’
c. /t/ after a verb ending in any voiceless consonant other than /t/
/pa:k/ - /pa:kt/, /mIs/ - /mIst/
‘park – parked’, ‘miss – missed’

4. MORPHEME, MORPH, ALLOMORPH (Cont….)
The other examples of allomorphs can also be found in the following examples:
Morpheme –s (plural marker) is represented by the following morphs:
a. /-Iz/ if a noun ends in alveolar or alveolar-palatal sibilant (i.e. consonant with a sharp, hissing sound).
fish – fishes, box – boxes , beach – beaches, bridge – bridges, etc.
b. /-s/ if a noun ends in a non-strident voiceless consonant (i.e. any one of the sounds / p t k f Ө /
cup – cups, leek – leeks, book – books, cart – carts.
c. /-z/ if a noun ends in a voiced nonstrident segment; this includes all vowels and the consonants /b d g d m n l r w j/
key – keys, shoe – shoes, mug – mugs, bag – bags, room – rooms,etc.