The antonyms for the phrase "was irresolute" can be described as determined, resolute, firm, certain, decisive, and resolved. These words suggest a sense of purposefulness and assurance in decision-making, unlike irresolute which implies hesitancy and doubt. Being decisive requires making a clear choice, without any hesitation or second-guessing. Similarly, being resolute and firm means having a strong determination to achieve your goals and stay on course. An irresolute person often lacks confidence and may be easily swayed by others. In contrast, a determined and resolved individual is more likely to achieve success and overcome challenges.