nicker
Concise Oxford English Dictionary © 2008 Oxford University Press:
nicker1
▶noun (pl. same) Brit. informal a pound sterling.
– origin early 20th cent.: of unknown origin.
Concise Oxford English Dictionary © 2008 Oxford University Press:
nicker2
▶verb (of a horse) give a soft breathy whinny. ▶noun a nickering sound.
– origin C16: imitative.
'nicker' also found in these Oxford entries:

