BE IN THE KNOW

English for Today by Ganiu Abisoye Bamgbose (Dr GAB)

BE IN THE KNOW

The meeting was held behind ~a closed door~ (nonstandard).
The meeting was held behind ~closed door~ (nonstandard).
The meeting was held behind closed doors (standard). If people have talks and discussions behind closed doors, they have them in private because they want them to be kept secret.

You should let ~bygone be bygone~ (nonstandard).
You should let bygones be bygones (standard). If two people let bygones be bygones, they decide to forget about unpleasant things that have happened between them in the past.

He has improved in ~leap and bound~ this season (nonstandard).
He has improved in leaps and bounds this season (standard). You can use in leaps and bounds or by leaps and bounds to emphasise that someone or something is improving or increasing quickly and greatly.
GAB