What Part of Speech is "Times"?

What part of speech are the operational words "plus", "minus", and "times"? This is a surprisingly tricky issue; apparently major dictionaries actually differ in their categorization. The most common classification is as some form of preposition -- the Oxford Dictionary says that they are marginal prepositions; "a preposition that shares one or more characteristics with other word classes [i.e., verbs or adjectives]".

Here's an interesting thread on Stack Exchange: English Language & Usage on the issue -- including commentary by famed quantum-computing expert and word guru Peter Shor:

Stack Exchange English Language & Usage:
Is “times” really a plural noun?