What does it mean to introduce a thought gradually and insidiously?

When a thought is introduced gradually and insidiously, it refers to a process where the idea is subtly implanted in a way that may not be overtly noticeable at first. This aligns closely with the concept of insinuating. Insinuation involves suggesting or hinting at something in a sly or indirect manner, which can lead to influence without explicit recognition by the individual receiving the idea.

In this context, the term captures the essence of how one might introduce a notion in a way that gradually takes hold, often because it is not presented outright but instead seeps in over time. This makes insinuate the most fitting choice among the options, as it denotes a subtlety that is characteristic of insidious introductions of thoughts.