antagonistic

/ˈænˈtægəˌnɪstɪk/

/æntægəˈnɛstɪk/

If you're antagonistic, you're hard to get along with. Harmony is not your friend — you prefer hostility and struggle.

If you're antagonistic to your little brother, you're always picking on him and giving him a hard time — causing him agony — a word that's buried in antagonistic. Even drugs or chemicals can be antagonistic: if you take a sleeping pill and then follow it with a few cups of espresso, the interaction is likely to be antagonistic. The sleeping pill and the caffeine struggle against each other and you're not likely to get much sleep.

Definitions of antagonistic

1. adjective

   characterized by antagonism or antipathy
   “slaves antagonistic to their masters”

   synonyms: adversarial, antipathetic, antipathetical

   hostile

   characterized by enmity or ill will
2. adjective

   incapable of harmonious association
   synonyms:

   incompatible

   not compatible
3. adjective

   arousing animosity or hostility
   “his antagonistic brusqueness”

   “Europe was antagonistic to the Unites States”

   synonyms:

   alienating

   causing hostility or loss of friendliness

   antonyms:

   conciliatory

   intended to placate

   appeasing, placating, placative, placatory

   intended to pacify by acceding to demands or granting concessions

   pacific

   promoting peace

   propitiative, propitiatory

   intended to reconcile or appease

   soft

   willing to negotiate and compromise
4. adjective

   indicating opposition or resistance
   synonyms: counter

   negative

   characterized by or displaying negation or denial or opposition or resistance; having no positive features
5. adjective

   used especially of drugs or muscles that counteract or neutralize each other's effect
   synonyms: incompatible

   antacid

   acting to neutralize acid (especially in the stomach)

   antiphlogistic

   counteracting inflammation

   antonyms:

   synergistic

   used especially of drugs or muscles that work together so the total effect is greater than the sum of the two (or more)