astrologist vs astrologer

astrologist and astrologer both are nouns.

Word	Noun	Adjective	Verb	Adverb
astrologist	Yes	No	No	No
astrologer	Yes	No	No	No

As nouns, astrologist and astrologer are synonyms defined as:

astrologist and astrologer: someone who predicts the future by the positions of the planets and sun and Moon

astrologist (noun)	astrologer (noun)
someone who predicts the future by the positions of the planets and sun and Moon	someone who predicts the future by the positions of the planets and sun and Moon