Is the difference in meanings between inobtrusive and unobtrusive enough to warrant a distinction in their use? Or are they interchangeable?
I would argue that they are interchangeable and that there is little variation in their meanings. In fact, it seems that inobtrusive is just a variation of unobtrusive, and many dictionaries cite unobtrusive as a definition for inobtrusive. According to Google Ngrams, the variant inobtrusive is almost nonexistent. The spellchecker for this very editor doesn't even recognize inobtrusive as a word. In general, I'd stick with unobtrusive.
They are just synonyms, inobtrusive being the less common variant as shown in Ngram.
- Not undesirably noticeable or blatant; inconspicuous.
- Not noticeable; unobtrusive.
Ngram: unobtrusive vs inobtrusive
prefix of negation, Old English un-, from Proto-Germanic "un".
The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words.
It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.