While Tolkien's discernment as a creative writer enabled him to dodge nearly-all the potentially most embarrassing examples of character naming; there remains the rather glaring problem that the names of the two main villains Sauron and Saruman - are too similar; so similar as to be confusing - and especially to the first time reader.
They certainly confused by 13 year old self, when I sometimes got them mixed-up - probably from my habit of inwardly pronouncing Sauron as "Sore-on", and Saruman as "Sore-mun".
So why did Tolkien make this error; why did he his two main "baddies" end-up with such superficially-similar names?
I don't know of any definitive evidence from Tolkien on this question; but I think we can infer a plausible, and probable, answer to this question.
If we can assume that Sauron's name arose first and had become fixed and non-negotiable during the writing of Lord of the Rings...
Then it is the naming of the later-arriving Saruman that needs to be explained.
Saruman is attributed to the the Anglo-Saxon/ Old English language which Tolkien ascribes to the Riders of Rohan as his feigned translation of the in-universe speech.
And in Anglo-Saxon "man" means man as in modern English - while the "Saru" element of the name refers to the word "searu".
I infer that it was the multi-faceted meanings and implications of searu that must surely have struck Tolkien as being so exactly right for the character of Saruman, that I suppose he "must have" been absolutely determined to keep this name, once he had thought of it.
...Even though it lead to a problem of similarity to "Sauron".
In Unfinished Tales, Christopher Tolkien gives the translation of searu as "skill, cunning, cunning device" - which perfectly captures the chief wizard's character:
"Skill": He was the most skilled of wizards; but also he was "cunning": tending to seeks his ends by dubious means - such as trickery, deceit, evasion; and "cunning device" references that Saruman was a clever maker of tools, contraptions, machines, artefacts...
An online Anglo-Saxon dictionary provides a longer list of alterative possible meanings and synonyms for searu:
1. war-gear, weapon;
2. armour; coat of mail;
3. device, contrivance; equipment;
4. 1) skill, art; ability; 2) stratagem, craft, artifice; trick.
Meanings 1 and 2 link-up with the later, corrupted, Saruman's building and equipping of a formidable army, intended to wage war upon Rohan.
My conclusion is that searu-man so perfectly captured the nature of the chief wizard, that the Anglo-Saxon Professor Tolkien simply could not resist sticking to the name Saruman!
Despite the problem that the word read too nearly the same as Sauron.
In this instance; Tolkien the philologist overcame Tolkien the creative writer.
