Adjective

(er)

showing clever resourcefulness in practical matters

artful, tricky or cunning

streetwise

*

knowledgeable

* {{quote-news

, year=2011 , date=November 10 , author=Jeremy Wilson , title=tEngland Under 21 5 Iceland Under 21 0: match report , work=Telegraph citation , page= , passage=The most persistent tormentor was Alex Oxlade-Chamberlain, who scored a hat-trick in last month’s corresponding fixture in Iceland. His ability to run at defences is instantly striking, but it is his clever use of possession that has persuaded some shrewd judges that he is an even better prospect than Theo Walcott. }}

(archaic) Scolding, satirical, sharp.

* 1599 ,

LEONATO. By my troth, niece, thou wilt never get thee a husband, if thou be so shrewd of thy tongue.

Adjective

(er)

Hard to grasp; not obvious or easily understood; barely noticeable.

The difference is subtle , but you can hear it if you listen carefully.

(of a thing) Cleverly contrived.

(of a person or animal) Cunning, skillful.

insidious

* 1623 , , act iv, scene 4,

Thy age confirmed, proud, subtle , bloody, treacherous.

Tenuous; rarefied; of low density or thin consistency.