The best replacement for preposition is adverb.

The best alternatives to preposition are rated as following:
★★★★★  adverb
★★★  conjunction
★★  particle
★  proposition
★  infinitive
★  subordinating conjunction
★  an adverb
  verb
  article
  adverbs
  participle
  an infinitive
  pronoun
  indirect object
  adverb particle
  as part of the infinitive
  determiner

Your alternative for preposition is not listed? Suggest!
Speaking about preposition, one probably shouldn't forget about gerund.

Other search terms related to preposition and their ratings are:
★★★★★ gerund
★★★ verbs
★★★ adjective
★★ verb
★★ noun
★ sentences
★ sentence
★ nouns
You have in mind a companion for preposition and it is not yet here? Propose!



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preposition
adverb
conjunction