What is a synonym for with?

Answer 1

The prepositions don't have synonyms.

There are several other ways you can phrase an expression that means "with" (depending on which meaning of "with" you have in mind; there are several), but you couldn't call them synonyms.

Some examples:

with (along with) - accompanying, escorting

with (next to) - alongside, amid

with (a trait or attribute) - having, displaying, possessing

with (affected object) - concerning, using, in regard to

with (on the same side) - supporting, promoting, in favor

with (by means of) - through, utilizing

(see the related link)