By descriptive word, I am assuming you mean an adjective.
Here is a list of one-syllable adjectives beginning with n, and there aren't many:
nice
neat
new
nude
numb
null
near
next
north (as in, "the north gate," "north wind," "north course")
night (as in, "a night nurse," "a night raid," "the night hours")
nuts (meaning insane or crazy, "She's nuts")
net (as in "net force," "net result," "net earnings")
Nash (meaning firm, stiff, hard)
naught (meaning lost, gone, ruined)
neap (low; this definition usually refers to tides)
necked (used in phrases like "stiff-necked." Can also mean "cracked.")
nerved (having nerves)
nesh (sensitive, tender, delicate)
nibbed (having a nib/point, or one of a certain kind, as in "broad-nibbed pen")
nigh (near or approaching)
nil (having no value or existence)
nine (amounting to nine in number)
ninth (next after the eighth; being one of nine equal parts)
no (not any; not at all; far from being, "he's no genius"; very little or negligible)
none (This is an archaic usage. It means not any or no.)
Norse (of or pertaining to ancient Scandinavia or its inhabitants; Norwegian)
nosed (having a nose)
now (encompassing the latest fads/fashions: "the now look")
nowed (knotted; tied in a knot)
nulled
used
Examples of one-syllable adjectives are:allbluecolddryeastfairgrandhotilljustkeylonemoreniceonepoorrawsafetruevilewholeyoung
cute or birds
etch
I do not believe there is one, I have researched and I think 2 is the most
The word "coy" is one syllable.
Yes the word skull is a one syllable word.
The word bruised only has one syllable. This means the whole word is the syllable and so there are no syllable breaks.
The word "gum" has one syllable.
The word "dread" has one syllable.
The word "past" has one syllable.
The word "strap" has one syllable.