The number 1. The first counting number and the smallest positive whole number.

Note the unusual spelling: 'one' starts with 'o' but the sound is /wʌn/ (like 'won'). 'One' can be used as a pronoun meaning 'a person': 'One should always be polite.' Article: 'a' or 'an one' → use 'a': 'a one-way street'.

'Number one' means the best or most important. 'One at a time' means doing things one by one, not all together. 'All for one, and one for all' is the famous motto of the Three Musketeers — meaning everyone supports each other.