hairdo vs hairstyle

hairdo and hairstyle both are nouns.

Word	Noun	Adjective	Verb	Adverb
hairdo	Yes	No	No	No
hairstyle	Yes	No	No	No

As nouns, hairdo and hairstyle are synonyms defined as:

hairdo and hairstyle: the arrangement of the hair (especially a woman's hair)

Other synonyms of hairdo include coif, coiffure, hair style.

hairdo (noun)	hairstyle (noun)
the arrangement of the hair (especially a woman's hair)	the arrangement of the hair (especially a woman's hair)