Grit in this colloquial sense originated in early 19th-century US English.
RELATED IDIOMS :
Grody to the max
unspeakably awful – US informal
Grody is probably an alteration of grotesque and to the max of to the maximum point.
in the groove = into the groove
performing well or confidently, especially in an established pattern
indulging in relaxed and spontaneous enjoyment, especially dancing – informal
A groove is the spiral track cut in a gramophone record that forms the path for the needle. In the groove is first found in the mid 20th century, in the context of jazz and it gave rise to the adjective groovy which initially meant playing or able to play jazz or similar music well.