DEFENITION OF ALLOMORPH AND ZERO ALLOMORPH

      allomorph is a variant form of a morpheme. Long and leng(th), for example, are allomorphs of a single morpheme. Adjective: allomorphic.
Depending on the context, allomorphs can vary in shape and pronunciation without changing meaning. The formal relation between phonological allomorphs is called an alternation.


An allomorph is one of two or more complementary morphs which manifest a morpheme in its different phonological or morphological environments.

Discussion
	The allomorphs of a morpheme are derived from phonological rules and any morphophonemic rules that may apply to that morpheme.

Examples (English)
	The plural morpheme in English, usually written as '-s', has at least three allomorphs:
	[-s] as in [hQts] 'hats' [-z] as in [d&u0254;gz] 'dogs' [«z] as in [bŒks«z] 'boxes'

Examples and Observations

• "[A]n underlying morpheme can have multiple surface level allomorphs (recall that the prefix 'allo' means 'other'). That is, what we think of as a single unit (a single morpheme) can actually have more than one pronunciation (multiple allomorphs). . . . We can use the following analogy:

  phoneme : allophone = morpheme : allomorph"

  (Paul W. Justice, Relevant Linguistics: An Introduction to the Structure and Use of English for Teachers, 2nd ed. CSLI, 2004)

• Complementary Distribution
      "The indefinite article is a good example of a morpheme with more than one allomorph. It is realised by the two forms a and an. The sound at the beginning of the following word determines the allomorph that is selected. If the word following the indefinite article begins with a consonant, the allomorph a is selected, but if it begins with a vowel the allomorph an is used instead . . .."
  
  "[A]llomorphs of a morpheme are in complementary distribution. This means that they cannot substitute for each other. Hence, we cannot replace one allomorph of a morpheme by another allomorph of that morpheme and change meaning."
  (Francis Katamba, English Words: Structure, History, Usage, 2nd ed. Routledge, 2004 

 Zero allomorph

                The symbol 0, indicating an absence of quantity or magnitude; nought,   (Former name)    cipher  

   the integer denoted by the symbol 0; nought  

      the cardinal number between +1 and --1  

   nothing; nil  

   a person or thing of no significance; nonentity  

   the lowest point or degree  
his prospects were put at zero     

     the line or point on a scale of measurement from which the graduations commence  

 

   The temperature, pressure, etc., that registers a reading of zero on a scale  

   the value of a variable, such as temperature, obtained under specified conditions  

      a gunsight setting in which accurate allowance has been made for both windage and elevation for a specified    range  

     (Maths)  

   the cardinal number of a set with no members  

   the identity element of addition  

     (Linguistics)  

  an allomorph with no phonetic realization, as the plural marker of English sheep

     allomorph with no phonetic realization, as the plural marker of English sheep  

   (as modifier)  
a zero form     

      (Finance, Also called)   zero-coupon bond   a bond that pays no interest, the equivalent being paid in its redemption value  
   Compare     →   Zebra  

 

      http://dictionary.reverso.net/english-definition/zero%20allomorph