a person that is useless,
troublesome or annoying, a fool.
From the english dialect "Git" or "Get" meaning "Gate". When using foundry sand to cast iron objects the access point for
the metal, that is
the funnel shape that lets the molten iron into the sand-mould was called the gate. This gate was of no use and would have to be removed from the final item and the item carefully finished to remove any blemishes caused by the gate. Thus the term "Useless gate (git)" was coined.