One from unknown herd rampaging through wrecked camp? (9)
I believe the answer is:
pachyderm
'one' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'unknown herd rampaging through wrecked camp?' is the wordplay.
'unknown' becomes 'y' (algebra).
'rampaging' is an anagram indicator.
'through' indicates putting letters inside (I've seen this in other clues).
'wrecked' indicates anagramming the letters.
'y'+'herd'='yherd'
'yherd' anagrammed gives 'hyder'.
'camp' with letters rearranged gives 'pacm'.
'hyder' placed within 'pacm' is 'PACHYDERM'.
'from' acts as a link.
(Other definitions for pachyderm that I've seen before include "Thick-skinned animal like elephant or rhino" , "Insensitive sort" , "One thick-skinned" , "Animal with very thick skin, elephant say" , "Thick-skinned mammal like elephant" .)