Tin and Fur are two possibilities.
calico, muslin, damask
total
wholesome
There is no word that can consist of 7 consonants and only have 3 letters. Consonants are letters.
snowday
sultana
The only English word you can make with those letters is oe.
Yes, protozoan is the only word you can make with those letters.
Strength is the only English word you can spell with those letters.
The only word I can think of for "joker", 3-letters, is imp.
Bree
Using only the first letters of a word to form a new word or phrase is called an acronym.