covert

Concise Oxford English Dictionary © 2008 Oxford University Press:
covert

▶adjective /ˈkʌvət, ˈkəʊvəːt/ not openly acknowledged or displayed. ▶noun /ˈkʌvət, ˈkʌvə/ 

• 1 a thicket in which game can hide.

• 2 Ornithology a feather covering the base of a main flight or tail feather of a bird.

– derivatives
covertly adverb,
covertness noun.

– origin ME: from OFr., ‘covered’, past part. of covrir (see cover).