Aphorism, n.
Etymology: [F. aphorisme, fr. Gr. Horizon.]
A comprehensive maxim or principle expressed in a few words; a sharply defined sentence relating to abstract truth rather than to practical matters. The first aphorism of Hippocrates is, "Life is short, and the art is long." Fleming.
Syn. -- Axiom; maxim; adage; proverb; apothegm; saying; saw; truism; dictum. See Axiom.
Shades of meaning
Fernald has no entry of its own for aphorism; he lists it under proverb.
Where he writes about it:
An aphorism partakes of the character of a definition; it is a summary statement of what the author sees and believes to be true. — from proverb
The aphorism is philosophical, the apothegm practical. — from proverb