This is due to reduction in number and/or size of the filiform papillae. A geographic tongue has localized areas of smoothening, but not sufficient to warrant use of the term Smooth tongue.
Synonyms:
exact_synonym:
Smooth lingual surface; Smooth surface of tongue
narrow_synonym:
Smooth dorsum of tongue
related_synonym:
Atrophy of dorsum of tongue; Atrophy of lingual surface; Atrophy of tongue surface