atto-
"atto" is a 4-letter English headword indexed on PlainSpell.
The verdict
“atto-” is uncommon English (outside the top frequency list), classed as a prefix. The kind of spelling people second-guess.
- Unranked
- below top-frequency English
- 5
- letters
According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - 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).
Corpus desk
Index EN-atto · atto- · English
atto- · unranked · 0 variants · 0 confusables
- FREQ-UNRANKED Unranked
- LEN-MID 5 letters
- VOW-2 2 vowels
- CONFUS-0 No pairs
- VAR-0 0 variants
- BOOK-THIN "A" thin
- PHOTO-UNK Peer pending
Read with this headword: Spelling guide for this pattern
Desk codes from Wiktionary headword shape, FrequencyWords rank tier, confusable-pair count, generated misspelling depth, letter-cohort book size, and photo-finish peer. Not a difficulty grade.
| Property | Value |
|---|---|
| Headword | atto- |
| Language | English |
| Part of speech | Prefix |
| Letters | 5 |
| Misspellings tracked | 0 |
| Confusable pairs | 0 |
| Source | Wiktionary (kaikki.org) |
Long-tail rank of “atto-” in English
Rare enough to double-check
atto- is uncommon English outside the top frequency list, classed as aprefix. Rarity is why readers land here mid-draft. Gloss: "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).".
We couldn't generate a plausible misspelling set for atto-, a sign its spelling follows regular English conventions. We don't track a confusable pairing for this entry, which usually means its spelling is distinct enough that readers don't reach for a similar-looking word instead.
Etymologically, the entry records: From Danish atten (“eighteen”), with reference to the (negative) exponent in the relevant power of ten; the same principle also explains femto-. The correct English form is atto-, spelled A-T-T-O--.
Definition
- 1In 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).
Etymology
From Danish atten (“eighteen”), with reference to the (negative) exponent in the relevant power of ten; the same principle also explains femto-.
Antonyms
This word in other languages
Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA). See the methodology for how each field is sourced and updated.