Something done obliquely is done in a roundabout way rather than directly. Asking your girlfriend if there's something else she'd rather wear to dinner is a way of obliquely telling her she doesn't look so great in what she's wearing.
The word obliquely can mean the indirect way something is talked about or the indirect path that something takes. It's also a word used to describe when something is positioned sideways or on a slant, like a ladder propped obliquely against the wall. Ever notice how the rain seems to fall on a slant against a lamp light at night? It's not falling straight, but obliquely or on an angle.
