Could vanda “oath, pledge, solemn promise” come from *WAD being a variant of WED "bind"? That could mean that *vasta- "pledge, promise" could be a variant of vesta- which was repurposed as "wed, marry" and derived from BES later in the game.
One notable feature of Sindarin is that it often uses adjectives adverbially, as in: noro lim, noro lim Asfaloth “run swift, run swift Asfaloth” (LotR/213). This can occur only when the adjective could conceivably be an attribute of the verb’s subject, as in this example where “swift” is applicable to the subject (Asfaloth). As Tolkien described it:
Comparison is Sindarin is a bit tricky. We have what appears to an intensive or superlative prefix ro- (< rau-) as in rovaed, which may mean “*very shapely” or “*most shapely” (PE17/147); this suffix seems to be the equivalent of Q. ar(i)- which elsewhere was described as “virtually superlative” (PE17/56).
There only two currently published questions in Sindarin (and none in its conceptual precursors): linnathol? “will you sing?” from 1969 (PE22/167) and man agorech? from the early 1950s (VT50/5), untranslated but almost certainly meaning “what have we done?” using the late-1940s, early-1950s 1st pl. inclusive pronominal suffix -ch (VT50/21-22). These two questions give us a fair amount of information, though.
The idea popped up on Vinye Lambengolmor that we could continue this fun project that we started on Google Plus but never finished.
We can discuss ideas here as we are progressing through the list (which is already quite advanced).
Here's the link to the spreadsheet: