Disingenuous

There's some words that I get a feel for the gist of their meaning, but never their exact meaning. Now I'm clearing some of those up in my study for the GRE. For example, there's "ingenuous", not to be confused with ingenious or cleverness. Rather, m-w.com defines ingenuous as showing innocent or childlike simplicity and candidness.

Example: My disingenuous, scheming roommate executed a diabolical plan today by inviting me on a nonstop two mile jog.

I want the aches in my legs to go away now.