must, mussed

Must or must describes an action that is imperative; something one ought to do, or should do-
We must do our homework before we watch TV.
You must be sure to unplug that before you remove the back.
Must is also used to express inevitability or certainty--
"Someday we all must die..."
There must have been a reason ...
Must is also used, informally, to mean something required or necessary--
The new phone is a must for the tech crowd.

Mussed or mussed ( rhymes with must ) is the past tense ( yesterday, or some time ago ) of "muss", meaning to make untidy or to leave in disarray--
She mussed her hair just before he took the picture.
His hair was mussed when he took off his hat.

Now that you know that, you can say--
"We must make sure that we don't leave the room mussed up; someone else will have to tidy it up if we do."

Note--"must" also means a kind of mildew or mold--
She didn't like the small of must in the basement.
"Musty" describes something that has mold or mildew on it--
What's that musty smell? We'll have to clean this with some bleach, or leave it in the sun.
"Mustier" is a comparative ( more or less than ) form of "musty"--
I washed it, but it smells even mustier.
Not to be confused with "muster", meaning to call or summon troops, or to assemble a troop-
The troops were ordered to muster at dawn.
"Mustered" is the past tense ( yesterday, or some time ago ) of "muster", meaning to assemble, or to be summoned to assemble--
The troops mustered at dawn.
Not to be confused with "mustard" ( rhymes with mustered ), the popular condiment--
Do you want mustard and ketchup on your burger?
Note # 2--"must" also means unfermented or new wine--
They tasted the must to determine if the wine would be good.
Note # 3--for trivia collectors, "musth" ( rhymes with must ) is a condition of frenzy or agitation that sometimes affects male elephants--
The elephants are not dangerous unless they are in musth.