astrologer vs forecaster

astrologer and forecaster both are nouns.

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

As nouns, forecaster is a hypernym of astrologer; that is, forecaster is a word with a broader meaning than astrologer:

astrologer: someone who predicts the future by the positions of the planets and sun and Moon
forecaster: someone who makes predictions of the future (usually on the basis of special knowledge)

Other hypernyms of astrologer include predictor, prognosticator, soothsayer.

astrologer (noun)	forecaster (noun)
someone who predicts the future by the positions of the planets and sun and Moon	someone who makes predictions of the future (usually on the basis of special knowledge)