Answer: ATTO

AnswerCrossword Clue
ATTOWord form for "one-quintillionth"
ATTOQuintillionth (prefix)
ATTOQuintillionth: Prefix
ATTOIt means "quintillionth"
ATTOPrefix meaning "quintillionth"
ATTOMetric prefix that's the reciprocal of exa-
ATTOQuintillionth: Comb. form
ATTOOne-quintillionth: Prefix
ATTOPrefix for 'quintillionth'
ATTOMetric prefix between femto- and zepto-