stew
Deny
deny
Cashew
Yes, you can make a casserole with those letters.
mars
No one word can be made from all of those letters, nor can any word that is more than four letters long.
swim, gym, him, Guam
No because a food chain ends with an animal eating another animal
Imagine you have four empty buckets in which to put any of the four letters Y, A, R, D into. At first you have four letters that can be placed in any of the four empty buckets. Once you've placed a letter in a bucket you only have three letters and three empty buckets to choose from. And so on... So there are 4x3x2x1 = 24 permutations of the word YARD.
baud, daub
Yes, there are. For example: moon, seen, soon, will.
No, the word 'PUNY' is the only word using that combination of letters, there are no words that start with or end with those four.