Language, vocabulary, phraseology, phrasing, diction, style are comparable rather than synonymous terms when they mean oral or written expression or a quality of such expression that is dependent on the variety, or arrangement, or expressiveness of words.
Language applies primarily to verbal expression with reference to the words employed. It may call attention to excellence or ineptness in the use of words, to their dignity or their vulgarity, to their fitness or lack of fitness, to their sonority or their stridency, or to any of the qualities which speech or writing may derive from the choice and arrangement of words.
Vocabulary calls attention chiefly to the extent or variety of the writer's or speaker's stock of words or to the sources from which such a stock is derived.
Phraseology or phrasing is sometimes used in place of vocabulary when the reader's attention is called especially to its idiomatic or peculiar character, but phraseology in particular stresses the grouping of words as much as their choice.
Diction calls attention to the choice and arrangement of words with reference to their expression of ideas or emotions. The term is used commonly of considered language (as of poetry, literary prose, or oratory) and it usually, therefore, implies selection or arrangement with reference to such ends as impressiveness, elegance, and beauty of sound.
Style denotes a mode or manner of expressing one's thoughts or emotions or imaginative conceptions in words, as distinct from or as distinguishable from the thoughts or emotions or conceptions expressed. It is sometimes thought of as a structure and diction peculiar to an age or a literary type and found in each representative work of that time and type, but perhaps more often it is thought of as a manner of expression which in structure and diction involves artistry but is individual and characteristic of its author.