Both Uses of

sheer
in
Brave New World

At their feet lay a straggle of low buildings, a criss-cross of walls; and on three sides the precipices fell sheer into the plain.
p. 107.6 *

sheer = so steep it is almost vertical

For the sake of the labourers; it would be sheer cruelty to afflict them with excessive leisure.
p. 224.8 *

sheer = pure (used for emphasis)

Definitions:

(1) (sheer as in: a sheer blouse)
typically of fabric: very thin and delicate -- often transparent
(2) (sheer as in: sheer fun)
complete or pure -- without restriction, qualification, or other elements (used for emphasis)
(3) (sheer as in: a sheer cliff)
so steep it is almost vertical
(4) (sheer as in: sheer to the left)
change direction; or to cause such a change of direction -- usually abruptly
(5) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Sheer can also be an alternative spelling for shear (to cut).