The so called “fleeting A” or “movable A” refers to the phonetic alternation in which short a makes appearance and loss in certain inflected forms of nouns.
Historically, Montenegrin did not tolerate any final consonantal clusters except: st, zd, št, žd, šć, žđ, šč, and dž, as they were often difficult to pronounce in the final position. Thus, in order to facilitate pronunciation a fleeting a was inserted. The following suffixes are especially prone to the rule – ac, ak, an, ar, at, anj, alj, ao, ac.
In Nominative, Accusative and Genitive singular and Genitive plural of masculine nouns:
A writer – pisac >pisca > pisaca
A young man – momak > momka > momaka
A dream – san > sna > snova
In Genitive plural forms of feminine nouns ending in a consonant cluster:
A sister – sestra > sestara
A notebook – sveska > svesaka
In Nominative singular indefinite masculine forms of adjectives and pronouns:
Short – kratak > kratki
Entire – sav > svi