We use 'tone' and consequently 'semitone' a lot in music - in Western music, the semitone is the smallest possible difference between two notes. (Not including guitar bends etc!).
However, the word 'tone' means several other things musical, so its use can be confusing. Where/when/why did the word actually come to mean the difference between C and D; F♯ and G♯, E♭ and F?
The word 'step' occurs from time to time - but that again is two half-steps. With the 12 tone system well in place now (or should that really be 6 tone..?) should there be a more apposite term we could use?
Funny - I tried 'tone' tag - and it's for a different 'tone'!