All 3 Uses of

discreet
in
Dracula

He is discreet and silent, and has grown into manhood in my service.
p. 24.3

discreet = trustworthy with secrets (or possibly sensible)

All men are mad in some way or the other, and inasmuch as you deal discreetly with your madmen, so deal with God's madmen too, the rest of the world. You tell not your madmen what you do nor why you do it.
p. 129.2

discreetly = trustworthy with secrets

Get to your bed and try to behave more discreetly.
p. 263.6 *

discreetly = in a manner that is unlikely to attract attention

Definitions:

(1) (discreet as in: discreet--not showy or gossipy)
trustworthy with secrets or subtle (not attracting attention)

This sense of discreet sometimes indicates that something is small (so as not to attract attention) as in "discreet earrings."
(2) (discreet as in: discreet--not foolish)
sensible and careful; possibly having good manners

This sense of discreet is more commonly seen in classic literature than in modern writing. There is may also refer to having the judgment to exercise good manners.