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be onto

B1 informal inseparable transitive
In simple words

To know that something important is there, or to have figured out what someone is really up to.

Meanings

1 B1 idiomatic informal

To have identified or discovered something important or promising.

"The scientists believe they're onto a new treatment that could change everything."

Grammar: inseparable
2 B1 idiomatic informal

To have realised or suspected what someone is up to, especially when they are doing something they should not.

"The customs officers were onto the smugglers long before the arrest was made."

Grammar: inseparable
3 B1 idiomatic neutral

To have recognised that something is a good idea or a winning strategy.

"With that new business model, they might really be onto something."

Grammar: inseparable
Usage notes

Largely interchangeable with 'be on to'. 'Be onto something' (discovering a lead or idea) and 'be onto someone' (suspecting them) are the most common patterns. Very natural in British and American English.

Commonly used with

something someone winner lead idea trick

Forms

Base
be onto
I/you/we/they
3rd person
is onto
he/she/it
Past simple
was/were onto
yesterday
Past participle
been onto
have + pp
-ing form
being onto
continuous

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