mas is a form of:

Ma



ជាពាក្យបំព្រួញនៃពាក្យ Master of Arts,
noun
1.
(COLLOQUIAL) (Male, mark[s], married, masculine, mass, measure, medium, maids [noon], mix, mince [mix], modification of, modules, month, mother, morning) ម៉ែ, ម៉ាក់
ENGLISH MEANING
noun
1.
A child's word for mother.
2.
In Oriental countries, a respectful form of address given to a woman; mother.
Conjunction
1.
But; -- used in cautionary phrases; as, "Vivace, ma non troppo presto" (i.e., lively, but not too quick).