A word for “man” as a male person, attested only as an element in compounds or as (archaic?) ndir (PE17/60). This word likely refers to male individuals of all races including Elves, Men, Dwarves and so forth, much like its Quenya cognate Q. nér. This word must have been derived from the primitive subjective form ✶ndēr of the root √N(D)ER “male person”, where the ancient long ē became ī, and the initial cluster nd- became d-, though the ancient cluster would still be reflected in mutated forms, such as in i nîr “the man” rather than ✱✱i dhîr.
Conceptual Development: Perhaps the earliest precursor to this word is (archaic) G. †drio “hero, warrior” with variants driw, driodweg and driothweg, a cognate of ᴱQ. nēr (GL/22). This Gnomish word was derived from primitive ᴱ✶n’reu̯, where the initial nr- became dr-. At this early stage, the root was unstrengthened ᴱ√NERE (QL/65), as reflected in (archaic) ᴱN. nîr “hero, prince, warrior-elf” in the Early Noldorin Dictionary of the 1920s (PE13/164).
> EN †dîr surviving chiefly in proper names (as Diriel older Dirghel [GYEL], Haldir, Brandir) and as agental ending (as ceredir “doer, maker”) ... In ordinary use EN has benn [for “man”] (properly = “husband”).
Thus in the scenario described in The Etymologies, dîr “man” was archaic and used only as an element in names or as a suffix. In ordinary speech it was replaced by N. benn, which used to mean “husband” but now meant “man”, while the word for “husband” became N. hervenn (Ety/BES). It is unlikely Tolkien imagined this exact scenario in later Sindarin, however, since the 1930s root for benn was ᴹ√BES “wed”, but by the 1960s the root for husband/wife/marry words had become √BER.
Neo-Sindarin: Since the status of N. benn is questionable given ᴹ√BES >> √BER, many Neo-Sindarin writers prefer to use S. ✱dîr as the Sindarin word for man. I am of the opinion that both dîr and benn are acceptable for “man, male person”. This is because I prefer to retain ᴹ√BES as the root for “marry, wed”, since it is the best basis for attested husband/wife words in (Neo) Sindarin.