Isobar, which means a line on a map connecting points having the same atmospheric pressure at a given time or an average over a given period.
Six letter words using the letters 'nuspiegn' are ensign, supine, and genius.
A six letter work is sicker.
fervor
NETHER
Versus.
tidies
iambus
LEGACY
onward
Accord is a six letter word. Accrue is another six letter word.
There are no English words that meet the criteria, even when you repeat the letters (which you need to do to make five letters spell a six-letter word).
alpaca