When it comes to describing a sly suggestion, there are many synonyms that can be used to convey a similar meaning. For example, terms such as "subtle hint," "insinuation," "veiled proposal," "innuendo," and "covert insinuation" can all be used to describe a suggestion that is made cunningly, and with an ulterior motive in mind. Other possible synonyms include "innuendo," "underhanded suggestion," "sneaky insinuation," "implicit suggestion," and "indirect proposal." All of these options describe suggestions that are not made directly or overtly, but rather in a sly, crafty manner.