allomorph

Noun
  1. Any of several different crystalline forms of the same chemical compound (synset 114844026)
    "calcium carbonate occurs in the allomorphs calcite and aragonite"
  2. A variant phonological representation of a morpheme (synset 106317596)
    "the final sounds of `bets' and `beds' and `horses' and `oxen' are allomorphs of the English plural morpheme"

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