Nanosecond (n.)

"’one-billionth of a second,’ 1959, from nano- + second (n.).” (etymonline.com)

Some scientists call a nanosecond a ‘light foot,’ since light can travel approximately one foot in one nanosecond!

Source: Vocabulary.com

Here is the word broken into its parts:

“second(n.1)

‘one-sixtieth of a minute of degree,’ also ‘sixtieth part of a minute of time,’ late 14c. in geometry and astronomy;

“Seconde, from Old French seconde, from Medieval Latin secunda, short for secunda pars minuta ‘second diminished part,’ the result of the second division of the hour by sixty (the first being the ‘prime minute,’ now simply the minute), from Latin secunda, fem. of secundus ‘following, next in time or order’).

“The second hand of a clock, the pointer indicating the passage of seconds, is attested by 1759.”

“nano-

introduced 1947 (at 14th conference of the Union Internationale de Chimie) as a prefix for units of one thousand-millionth part (now ‘one-billionth’), from Greek nanos ‘a dwarf.’

According to Watkins, this is originally ‘little old man,’ from nannos ‘uncle,’ masc. of nanna ’aunt’ (see nana), but Beekes calls it ‘An onomatopoeic word of unknown origin.’

Earlier nano- was used as a prefix to mean ‘dwarf, dwarfish,’ and still it is used in a non-scientific sense of ‘very small.’”

Source: etymonline.com