postfix(n = noun.communication) suffix - an affix that is added at the end of the word;
is a kind of affix, ending, termination

   A letter, syllable, or word, added to the end of another word; a suffix. Parkhurst. [1913 Webster]

   To annex; specifically (Gram.), to add or annex, as a letter, syllable, or word, to the end of another or principal word; to suffix. Parkhurst. [1913 Webster]

postfix, n. & v.
--n. a suffix.
--v.tr. append (letters) at the end of a word.

postfix notation