There are three 7-letter words possible:
jovial
sultana
snowday
jetsam
Except you gave us 11 letters that spell "celebrating."
Those letters can be used to spell "exigent".
Six letter words using the letters 'nuspiegn' are ensign, supine, and genius.
Breeder is a 7 letter words using only those letters
Using all 7 letters you get rewords
You can not spell any 4 letter words with the 3RD letter N using only the letters pmhlijkssxt. The letters do not include the letter N.
Here are some four (4) letter word using the letters, mighuesn: menu. smug. mien. mine. muse. semi. sing. sign. sung. hems. hung.
'PROSCENIUM' itself is the only 10-letter word using those letters. There are several 8-letter words, but no other 10-letter ones.