Antonyms of "put on guard" include "put at ease," meaning to make someone feel relaxed and reassured, or "disarm," meaning to strip away someone's defenses. Other antonyms could include "unfazed," meaning to remain calm and unbothered, or "unaware," meaning to not be conscious of potential threats or danger. Additionally, "distract," meaning to divert someone's attention, or "comfort," meaning to provide emotional support, can also serve as opposite meanings to "put on guard." Overall, these antonyms suggest a sense of ease and relaxation, rather than a heightened state of alertness and caution.