Atto-

prefix

prefix ·Rare ·Advanced level

Definitions

Prefix
  1. 1
    In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10⁻¹⁸ (short scale quintillionth or long scale trillionth). morpheme

Antonyms

All antonyms
exa

Etymology

From Danish atten (“eighteen”), with reference to the (negative) exponent in the relevant power of ten; the same principle also explains femto-.

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.