@Randal'Thor the short answer is that any rhetorical device is technical, not semantic; a simile, or a metaphor, or an epithet, or alliteration, is defined strictly in terms of how it operates, not in terms of what it means. The meaning is always context-dependent. I've
revised the last three paragraphs of the answer and I hope it's clearer now. If not, let me know. Thanks for helping me make the answer better.