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3. be on to

be on to

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be on to

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 also: on

be on to

Informal

To be aware of or have information about: You'll never deceive us again; we're on to you.

See also: on