semitone vs half step

semitone and half step both are nouns.

Word	Noun	Adjective	Verb	Adverb
semitone	Yes	No	No	No
half step	Yes	No	No	No

As nouns, semitone and half step are synonyms defined as:

semitone and half step: the musical interval between adjacent keys on a keyboard instrument

semitone (noun)	half step (noun)
the musical interval between adjacent keys on a keyboard instrument	the musical interval between adjacent keys on a keyboard instrument