Both Uses

discreet
in
The Hunt for Red October
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"That can be arranged, sir, but it will have to be discreet," Moore cautioned.†
Chpt 16.
The carrier battle groups would be following them all the way to Iceland, keeping a discreet distance and maintaining air groups at the fringe of their radar coverage continuously, just to let them know that the United States still cared.†
Chpt 17. *

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.
(3) (meaning too rare to warrant focus)