# N1 vs NB

> English confusable word pair

## The two words

### N1
*noun · frequency rank #30,893*
The rotational speed of the low-pressure spool of a multiple-spool gas turbine engine, expressed as a percentage of a certain reference rotational speed.

### NB
*phrase · frequency rank #17,908*
Initialism of nota bene; used in written English to introduce something to be noted.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/vs/n1-vs-nb