All verbal communication has two features: the words, vocabulary; and the way the words are structured, what could be called syntax. There are conventions associated with both vocabulary and syntax, and they can be strictly adhered to or not, depending on the nature of work. In academic papers sentences that conform to the conventions of formal writing and ‘acceptable’ vocabulary are usually demanded. (You won’t find writing like this in an academic journal: “The Bard is fucking brilliant. You gotta just love the way be screws with our heads with them kinky plots of his.”)
In poems on the other hand, there are no ‘unacceptable’ conventions regarding syntax or vocabulary. The poet may choose to follow the metric and rhyme scheme conventions of, for example, a sestina or sonnet, or instead just devise a new one—or even reject all conventions. Likewise with vocabulary, with word choice. There are no unacceptable words. Foreign words, made-up words, slang, vulgarities, all are acceptable. And all appear in great poems. Yet there remain those who believe these aren’t ‘poetic’.
Poetry prudes think all dictionaries, other than the first edition of the OED, are Pandora Boxes, when actually they are treasure chests for a poet. I love finding new words to add to my writer’s toolbox. I love dictionaries of vulgarities, philosophical terms, street slang, imported words, and especially scientific terms. It is this last that seems to be most underutilized. I derived great pleasure in combining the rich vocabulary of science with earthy language in my book, The Sad Science of Love. (Shameless plug)