insidieux /ɛ̃sidjø/ adjective C2 le (masc.) la (fem.) Underline = a spelling pattern that usually signals that gender. Adj Register Neutral Era Current Frequency Rare Domain General Tone Neutral Word fingerprint: Register: neutral. Era: current. Frequency: rare. Domain: general. Connotation: neutral. Meaning 1 insidious, treacherously gradual La maladie progresse de façon insidieuse. The disease progresses in an insidious way. Similar words dangereux Dangereux (dangerous) overlaps with insidieux (insidious) -- an insidious threat is dangerous precisely because it creeps up gradually, unnoticed. Practice 1 What does insidieux mean? English finite courteous insidious insidious, treacherously gradual 2 Which fingerprint chart matches insidieux? Adj Register Neutral Era Current Frequency Common Domain General Tone Neutral Word fingerprint: Register: neutral. Era: current. Frequency: common. Domain: general. Connotation: neutral. Adj Register Neutral Era Current Frequency Core Domain General Tone Neutral Word fingerprint: Register: neutral. Era: current. Frequency: core. Domain: general. Connotation: neutral. Adj Register Neutral Era Current Frequency Rare Domain General Tone Neutral Word fingerprint: Register: neutral. Era: current. Frequency: rare. Domain: general. Connotation: neutral. insidieux: neutral register, rare frequency, general domain, neutral connotation. adjective Last updated 2026-10-08