IPA: /ˈæn.ti.wɔːr/
KK: /ˈæntiˌwɔr/
Opposed to war or to a specific conflict, often involving protests or political positions against military actions.
The antiwar movement gained momentum during the Vietnam War.
Antiwar is formed from "anti-" (meaning against) and "war" (from Old English "werre", meaning conflict or battle). The word describes a stance or movement that opposes war.
Think of being 'against' ('anti-') conflict or battle ('war') — that's what antiwar means.