Eidolon :: Eidolon (n.) An image or representation; a form; a phantom; an apparition.
Orchidology :: Orchidology (n.) The branch of botany which treats of orchids.
Pteridology :: Pteridology (n.) That department of botany which treats of ferns.
Tidology :: Tidology (n.) A discourse or treatise upon the tides; that part of science which treats of tides.