失 is a formal/literary verb that covers a range of meanings around losing, missing, and failing. You often see it in fixed compounds like 失去 (to lose), 失败 (to fail), 失信 (to break a promise), and 失误 (to make a mistake). Unlike 丢 which is more colloquial, 失 is used in serious or abstract contexts. As a verb it can take objects: 失机会 (miss an opportunity), 失约 (break an appointment). Note that some senses in the dictionary gloss (like 'mishap') are noun uses that appear in compounds such as 过失 or 失误, not as standalone verbs.