The story
* Shortened from Michael (Male). * Shortened from Michel (Male). * Shortened from Michelle (Female). These names originally a variant of Hebrew: מי כאל (Michael). In Hebrew pronounce as (Miha'el), and short version is מי כ (Miha). But in other countries, due to dialect, the short version began to be pronounced as (Misha), and so a shorter version appeared as (Mish).
Etymology from Wiktionary, CC BY-SA 4.0.