 The rule is that the last vowel of a succession of syllables that end in a short vowel is dropped, for example the declinational root of the verbal adjective of a root PRS is "PaRiS-".Thus the masculine singular nominative is "PaRS-um" (< "*PaRiS-um") but the feminine singular nominative is "PaRiStum" (< "*PaRiS-at-um").Additionally there is a general tendency of syncope of short vowels in the later stages of Akkadian.