Cham

English dialects provide a shocking array of variety as well as being time-bubbles that preserve otherwise ancient traits. West Country English is one such, that gives us a shortening of the first person singular.

In the Middle English period, the first person singular pronoun, "I" had an older form "Ich" - itself from the Old English ic, cognate to words such as he German "Ich", which the medieval form coincidentally resembles, and Scandinavian "jeg/jag".

Just like we in modern English have ways of contracting "is/are/am" with the pronouns that precede it, i.e. "I'm", West English of this period also had, "Icham", which later got shortened to "cham" in modern times.

It sadly seems to have died out, but it belongs to that elusive group of rare shortened forms of "I am", which includes "amn't", itself the forefather of "ain't", and the Scottish "amnae".