Prosaic, prosy, matter-of-fact all denote having a plain, practical, unimaginative, unemotional character or quality.
Prosaic implies an opposition to poetic in the extended sense of that word. Although the term suggests the quality of prose, it seldom refers to literary prose as such but rather to the ordinary language of men in communicating their wants, their ideas, or their experiences, or in rendering intelligible what is difficult to understand or make clear; hence, prosaic usually implies a commonplace, unexciting quality, and the absence of everything that would stimulate feeling or awaken great interest.
Prosy, on the other hand, suggests a relation to prose, the verb, rather than to prose, the noun, and heightens the implication in the verb of turning what is poetry or interesting prose into dull plain prose (as by paraphrasing or by translating).
Consequently, prosy stresses extreme dullness or tediousness and usually implies a tendency to talk or write at length in a boring or uninviting manner.
Matter-of-fact stresses a lack of interest in the imaginative, speculative, visionary, romantic or ideal; sometimes it connotes accuracy in detail, but often it suggests concern only for the obvious and a neglect of the deeper or spiritual reality or an absence of emotional quality.