Is for fear of a preposition?

Answer 1

Yes. The words "for fear of" are an idiom, a compound preposition synonymous with the participle "fearing." It forms adverbial prepositional phrases.

The words for and of are both separately prepositions, while fear is otherwise a noun or verb.

Answer 2

The rule against ending sentences with prepositions is a holdover from Latin grammar rules that were applied to English. However, it is now widely accepted that it is acceptable to end a sentence with a preposition in English. Instead of forcing awkward sentence structures to avoid ending with a preposition, it is more important to prioritize clear and natural communication.