I don’t know any specific name for it, but it is fairly common reading technique used in literary analysis. If you ready any kind of poetry more refined (say [1] or [2]) in its internal structure, it is an absolute necessity.

It is quite amazing how many people do not know that there is a multitude of reading techniques to be used with various kinds of texts. You need to use a right tool for the job. Tolkien’s passages describing the Middle Earths ecological landscape are particularly rich calling for careful reading and lingual analysis. I believe he uses almost sole old Celtic words in those passages, avoiding any newer latin-based words more familiar to a modern reader, which cannot be a coincidence.

[1] https://www.poetryfoundation.org/poems/46452/to-an-athlete-d... [2] https://poets.org/poem/having-coke-you