In the phrase “move out of the way”, what is the part of speech of the word “out”? of the word “of”?
There are good reasons for not slavishly struggling to place every orthographic word into a word class.
For instance, idioms are probably often best treated, at least in part, as 'units of meaning', so 'he kicked the bucket' in the idiomatic sense can't be adapted to 'they kicked the buckets', but can be adapted to 'they soon kicked the bucket'. There is a degree of compositionality.
Again, it seems senseless to try to unequivocally label front as 'adjective' or 'noun' in front line (units) when your neighbour chooses to write the compound adjective frontline. Crystal labelled 'units of meaning' lexemes; compounds, whether closed, hyphenated or open, would be single lexemes.
It has been said that prepositions straddle the dividing line between lexical and function words. Certainly, out of in move out of the way has semantic weight and could easily be illustrated in a cartoon. It is arguable whether there is more of a 'two-concept' flavour with 'out of' (compare 'into', which combines an 'inness' and a 'getting there') than with 'in between' (which just means 'between'); however it is often classed as a compound preposition:
The following is found at http://www.ehow.com/info_8487966_compound-prepositions.html :
Compound prepositions are prepositions that are composed of two or more words. They are used in the same way that simple prepositions are used to show a relationship between a noun or pronoun and another word in the same sentence. Some examples of compound prepositions include "in between," "instead of," "in front of" and "out of." An example sentence: "The cat leapt out of the brown box," "out of" being the compound preposition.