fluid ounce
Concise Oxford English Dictionary © 2008 Oxford University Press:
fluid ounce
▶noun
- 1 Brit. a unit of capacity equal to one twentieth of a pint (approximately 0.028 litre).
- 2 (also fluidounce) US a unit of capacity equal to one sixteenth of a US pint (approximately 0.03 litre).
'fluid ounce' also found in these Oxford entries:

