By the sly

in a sly or secret manner.

See also: Sly

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Specifically, the dispatch revealed Jamshaid 'JD' Chaudhry's insight into a live demonstration of CANARES by the Sly Fox Mission 22 rapid prototyping team in September, sponsored by Naval Surface Warfare Center Dahlgren Division (NSWCDD).