1. To determine, discover, or come to understand something. A noun or pronoun can be used between "suss" and "out." I spent the entire class trying to suss out the meaning of the poem, but I just couldn't get it. It took him a little while, but he sussed it out eventually. We've sent our best operatives to suss the enemy's intentions out.

2. To observe and form an opinion about or estimation of someone or something. A noun or pronoun can be used between "suss" and "out." I strolled around the arena sussing out the competition. I always insist on test-driving a car to suss it out before I'm willing to spend any money.