What part of speech is the word fluency?

Answer 1

fluency
the part of speech: Noun.

when it comes to telling whether a word is adjective,noun or verb,etc.it is not always possible and easy to tell what part of speech the word belongs to unless it is put in a sentence "context".still,the word "fluency" is a noun because it cannot be anything else than a noun.(not ambiguous)
anyways,there are some reliable prototypical forms that some parts of speech have.if the word concerned does not have such prototypical "affixes",then they need a context.
e.g
mother/kindly/well...
one cannot tell to what part of speech these words belong in that they are totally ambiguous.so we can say "she mothered him for seventeen years"see,this is not a noun (which was your first guess).rather,it is a verb.
"he is well" "you work well".the first "well" is an adjective whereas the se cond one is an adverb (modifies the verb TO WORK).
"he was treating me kindly"adverb (see the protorypical suffix "ly") but "he has a very kindly daughter) adjective.now you see why you need the sentence "context" in which the word is put ?
important:one cannot just tell that a word belongs to any certain part of speech without justifying why it does belong to it.this is not difficult,yet has rules.

Answer 2

The word "fluency" is a noun. It refers to the ability to speak or write a language easily and effectively.