rezerwowy in English:

I substitute honey for jam.

He's my substitute for the next month.

Books are good enough in their own way, but they are a mighty bloodless substitute for life.

It is impossible to substitute machines for people themselves.

After a while, my father got angry and said “It seems your wife will not stoop to being a substitute writer!”

Moreover, for your safety, we advise use of a substitute email address.

We encounter similar difficulties when we substitute rectangles for triangles in this configuration.

Then I'll work on the principle that deference is no substitute for obedience.

Only three substitutes are allowed to enter the pitch.

During the Cold War, the U.S. ramped up research on drones, hoping to use them as substitutes for manned spy planes.

Why don’t you substitute one hour of watching TV a day for one hour of exercise?

Can we substitute this old products by new ones?

We can substitute the bacon for cheese, if you like. (= We can give you cheese instead of bacon)

A substitute is sth that replaces another thing.

ASCII quotes are a substitute character for the “real” quotes that vary from language to language, and the advent of Unicode have rendered ASCII quotes obsolete.

Tom and Mary were my backup singers back when I used to perform.

It's wise to make data backup on your computer every now and again.

There was a backup on the highway because of an accident.

Bring backup. Have you made a backup of that document?

There must be another backup.

It’s a good idea to save this file as backup.

Jane radioed the dispatcher for backup.

No problem. If X happens, we have Y as a backup.