Swear by Definition 1 of 2Pro Tip 1/3Personal Recommendation Used when confidently suggesting something based on personal experience. For quick meals, I swear by these instant noodles. Pro Tip 2/3Conveys Trust Expresses a strong belief in the reliability or effectiveness of something. When it comes to security, I swear by this alarm system. Pro Tip 3/3Not Always Literal Often used figuratively, not indicating literal swearing or oaths. I don't often cook, but I swear by my grandma's recipes.