The insidious spread of invasive algae across the coral reef went unnoticed for months, slowly choking the native marine life before divers detected the damage.
入侵藻类在珊瑚礁上的隐蔽蔓延数月未被察觉，慢慢扼杀本地海洋生物，直到潜水员发现损害。
Which choice best defines “insidious”?
A — Proceeding harmfully but stealthily.. “insidious” means Proceeding harmfully but stealthily..
Which word means “Proceeding harmfully but stealthily.”?
C — insidious. “insidious” means Proceeding harmfully but stealthily..
insidious — Proceeding harmfully but stealthily.. In Chinese: 阴险的；暗中危害的.
insidious is pronounced //ɪnˈsɪdiəs//.
The insidious spread of invasive algae across the coral reef went unnoticed for months, slowly choking the native marine life before divers detected the damage. (入侵藻类在珊瑚礁上的隐蔽蔓延数月未被察觉，慢慢扼杀本地海洋生物，直到潜水员发现损害。)
stealthy, subtle, sneaky — all close in meaning to insidious (Proceeding harmfully but stealthily.).
overt, blatant — each the opposite of insidious (Proceeding harmfully but stealthily.).
Yes. insidious is on the SAT Prep Difficult list — the higher-register words that decide the hard questions. The Digital SAT does not test vocabulary in isolation; words like this one are tested through Words in Context questions, where you choose the word that completes a passage most logically and precisely.
in- + sid(坐) → 暗中埋伏 → 潜伏为害。