Mas

In Japanese, conjugation is fundamental to piecing words together with auxiliaries. For example, to express the polite past, we must first take the "ren'yōkei", or "continuative", conjugation of a given verb and attach it to the auxiliary ます (masu). When we do this with a verb such as のむ (nomu), it becomes のみます (nomimasu), at first. This is the polite form, as ます forms the polite. To properly express the polite past in full, we must add the auxiliary た. The stem of ます (masu) is a simple "mas-" sound. Since it ends with an S sound, a change occurs when we attempt to add た. The resulting "masta" is difficult to pronounce and not easy to write in Japanese, as it neglects the common consonant-vowel spelling rule. So, a compromise is made, also known as an 音便 (onbin), or, literally, a "sound convenience". The "masta" takes on an I sound between the stem's end and the auxiliary's beginning. Since there is no "si" in Japanese, "shi" is used instead. The resulting conjugation is のみました (nomimashita). When pronounced, it may be contracted and read as "nomimash'ta".

Source: tatoeba (12652385)

When she was pregnant with her second child they ran away to France and played at being artists in a secluded mas near Avignon – two months of bliss.

Source: wiktionary

Ward, who was best known for his winning portrayal of George Bailey’s Cylindul the Sun God from the Golden City of Palengue, became a staple on the mas circuit up until the 1990s, lending his support to the likes of Peter Minshall and others.

Source: wiktionary

Aming was a recipient of the Humming Bird Silver for his contribution to the vibrancy of T&T mas in 1996.

Source: wiktionary