Dotty, Rose & Dave shunned Oscar. Hostile! (7)
I believe the answer is:
adverse
'hostile' is the definition.
(I've seen this before)
'dotty rose dave shunned oscar' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'dave' is 'adve' which is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for adverse that I've seen before include "Conflicting" , "Evaders being harmful" , "Opposed - inauspicious - opposite" , "Unfavourable - red vase (anag)" , "Dire" .)