One in terrible desert must be moved somewhere else (2-5)

'else' is the definition.
Both the answer and definition are adjectives.
Perhaps you can see an association between them that I can't see?

'one in terrible desert must be moved somewhere' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
an anagram of 'desert' is 'rested' which is present in the left over letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?