clug
Jolly is another five letter word meaning merry or happy is another.
You can make CLERIC
Acronym
Add another letter. men, met
It is called a "letter manipulation" or a "word transformation."
Anagram
aver
forced
If you rearrange the letter of EIGHTH, you can make the word HEIGHT
Change the A to a T to make "SOFT". Change the F to a M to make "SOMA"
Richen.
You can change the 'm' to a 't' to make wart.