All I can say is that
Parf Edhellen still includes it under their
Sindarin section, albeit (just noticed) with an
asterisk, about which the site explains:
"These exist to inform you that the gloss originate from a source which might be outdated or questionable."
The source for
maidh [Tolkienian at least] would seem to be
Etymologies. And generally speaking, in the sphere of Neo-elvish word-making, there have been Noldorin words that have been [again generally] accepted into Sindarin, as long as the phonology fits, and nothing published later appears to create a problematic scenario . . .
. . . so here I'm
assuming [!] that if anything new makes this problematic, that someone at PE would have taken it out "by now", or at least warned the reader beyond the general "asterisk warning."
Unless I missed something, there's no MAD- or
maidh in
Words, Phrases and Passages [post Lord of the Rings], but again, maybe there's some other source that provides some argument that this word simply cannot exist in the updated linguistic scenario.
I only [happily] dabble in the
Elvish tongues and nomenclature.
No expert me