Apple built in OS X Dictionary:

word: a single distinct meaningful element of speech or writing, used with others (or sometimes alone) to form a sentence and typically shown with a space on either side when written or printed.

If you look at that definition and then at the following sentence:

NASA launched a shuttle today.

Means NASA, an abbreviation is used as a word, in place of a number of words. So yes an abbreviation is a word.

Apple built in OS X Dictionary:

word: a single distinct meaningful element of speech or writing, used with others (or sometimes alone) to form a sentence and typically shown with a space on either side when written or printed.

If you look at that definition and then at the following sentence:

NASA launched a shuttle today.

Means NASA, an acronyn, is used as a word, in place of a number of words. So yes an acronym is a word.