Slightnesses are subtle, small, or minor occurrences that do not leave significant impacts. The antonyms or opposite words for slightnesses are weightiness, seriousness, importance, and magnitude. Weightiness is the quality of being significant or having a great impact, while seriousness refers to the quality of having deep thoughts, concern, or significance. Importance and magnitude, on the other hand, are the scale, value, or degree of impact that a phenomenon or occurrence can have. When these antonyms are used in place of slightnesses, they signify the gravity, relevance, and significance of an event or issue.