backing, support, supplement, extra, addition
The word incidentally means "by the way" or "of a minor nature".
accompanying
See the accompanying answer:
The word 'accompanying' is the present participle of the verb to accompany.The present participle of the verb is also a gerund, a verbal noun.The present participle of the verb is also an adjective.Examples:Verb: I will be accompanying the children on the class trip.Noun: Accompanying will be Miss Bea Taylor on the piano.Adjective: The suite includes an accompanying terrace.
They are synonyms.
Synonyms
Relative and kin are synonyms.
accompanying
storage
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)
They are synonyms.
synonyms