Mode of Elvish verse (UT/146; WJ/311). Its final element is thent “short”, but the meaning of the first element minlamad is unclear. It may perhaps mean “first-echoing” and refer to alliteration, as suggested by Patrick Wynne and Carl Hostetter (Tolkien’s Legendarium, p. 121-2). Tolkien said “this verse was not wholly unlike the verse known to Aelfwine” (WJ/311) and this may refer to the Old Norse or Old English styles of alliterative poetry; hat tip to Ellanto for suggesting this to me. In the Unfinished Tales as originally published, Christopher Tolkien gave this phrase as Minlamed thent/estent (UT/146), but in The War of the Jewels he said this was a slip on his part, and that J.R.R. Tolkien actually wrote Minlamad (WJ/311 and p. 315 note #3).
Sindarin
minlamad
noun. 'first voiced' or 'first-echoing', alliterative (?) verse mode (minlamad thent/estent)
minlamad
noun. ?alliteration, (lit.) first-echoing
minlamad thent
proper name. mode of Elvish verse
The word is not translated by Tolkien. For a discussion of its probable meaning, refer to Tolkien's Legendarium p. 121-122