Trig
There are no English words you can make using only those letters.
Breeder is a 7 letter words using only those letters
You can only spell using letters!
Using only the first letters of a word to form a new word or phrase is called an acronym.
snowday
sultana
There is only one word that can be formed using all 7 letters provided. The word that is formed is "saltbox". There are many other words that can be formed using those letters that are 6 letters or less.
Using the letters abcdefg you can spell a few 5 letter words. Badge, caged and faced are words spelled using the letters abcdefg.
Just about anything. Math can describe things, but it's not the only way to describe things.
Installs - however this is eight letters long
jetsam