pico-
Concise Oxford English Dictionary © 2008 Oxford University Press:
pico- /ˈpiːkəʊ, ˈpʌɪkəʊ/
▶combining form denoting a factor of 10−12: picosecond.
■ very small: picornavirus.
– origin from Sp. pico, lit. ‘beak, peak, little bit’.
'pico-' also found in these Oxford entries:

