As nouns the difference between atter and sheer
is that
atter is while
sheer is (nautical) the curve of the main deck or gunwale from bow to stern.
As an adjective sheer is
(textiles) very thin or transparent.
As an adverb sheer is
(archaic) clean; quite; at once.
As a verb sheer is
(chiefly|nautical) to swerve from a course.