The term nibble originates from the fact that the term byte is a pun on the English word bite. A nibble is a small bite, or half a bite. The nybble spelling parallels the spelling of byte.
Many references suggest that both "nibble" and "nybble" represent 4 bits or half a bite. Others maintain that 1 nybble represents 8 nibbles in the same way that 1 byte represents 8 bits.