General Synonyms:
* Aggressive
* Antagonistic
* Unfriendly
* Unwelcoming
* Adverse
* Inimical
* Opposed
* Unfavorable
* Warlike
* Bellicose
More Specific Synonyms:
* Angry (emphasizes emotion)
* Bitter (emphasizes resentment)
* Dangerous (emphasizes threat)
* Enemy (emphasizes opposition)
* Malicious (emphasizes intent to harm)
* Ruthless (emphasizes lack of mercy)
* Vicious (emphasizes cruelty)
Informal Synonyms:
* Mean
* Nasty
* Unpleasant
* Bad
The best synonym to use depends on the specific situation and the meaning you want to convey. For example, if you're talking about a hostile environment, "unfavorable" might be a good choice. But if you're talking about a hostile person, "aggressive" might be more appropriate.