coin?
vary
If the word has four letters, "mean" would work.
There isn't a synonym for the word trust that is four letters. But try, hope or love.
A synonym for fable (4 letters, beginning with M) is myth.
aitch
A synonym for specimen is sample
Well, honey, the synonym you're looking for is "dire." It may not sound like a ray of sunshine, but it fits the bill with four letters and ending in "ire." So, there you have it, no need to sugarcoat it!
nasty
twirl
synergy
hare
A synonym for metamorphosis is change.
A synonym for varied is diverse.