INSID'IOUS, adjective [Latin insidiosus, from insideo, to lie in wait; in and sedeo, to sit.] 1. Properly, lying in wait; hence, watching an opportunity to insnare or entrap; deceitful; sly; treacherous; used of persons. 2. Intended to entrap; as insidious arts.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI