1
general::
1. Be aware of or have information about, as in They can't pull that trick again; we're on to them now. [Colloquial; second half of 1800s] 2. Discover something important or profitable, as in The researchers claim they are really on to something big. [Colloquial; mid-1900s], see BE ON TO. on top In a dominant or successful position. It is Also put as come out on top, as in As we expected, Paul again came out on top in the chess tournament. [Mid-1500s] Also see ON TOP OF.
American Heritage Idioms