In this post from a Facebook group, somebody asked what the difference is between the words tio, tia, pai, and mai. The conclusion in this discussion was that all these words mean the same thing but that pai and mai are used by Chabacano speakers who live in the countryside or rural areas.
The same words (with the same pronunciation) exist in Portuguese and they mean father (pai) and mother (mae).
In this article about Puerto Rican Spanish, it is said that "Puerto Ricans also often shorten words by eliminating whole syllables. A good example are the words para, madre, and padre ("for", "mother", and "father"): Puerto Ricans may pronounce para as /pa/, madre as /mai/, and padre as /pai/.
If you ask me, I think the original meaning of these words are mother and father (originating from Spanish or Portuguese) but somehow the meaning just got obscured. How it got obscured though is beyond me. Sadly, this is one of the many lexical items that are slowly disappearing from the Chabacano language. Personally, I haven't heard anyone aside from the people in my father's family use these words.