Cash, from
Malay kasi, is the traditional English name for a Chinese coin - the kind that is round with a hole in the middle through which it can be strung. One cash is one coin, usually one
copper coin unless otherwise specified.
Strung cash were traditionally stored and spent in units of fifty or a hundred cash. The traditional Chinese word was simply
qian2 in
Mandarin.
The name cash is unfortunate, because it looks and sounds the same as the unrelated English word for "ready money". And oddly the modern Chinese word qian2 now means "money" in general, not coin. Thus both the Mandarin and English names for this thing now sound as if they mean money in general.
A number of traditional English words for Chinese things originate in Malay - evidently they date from Captain Cook's time.