革 is a bound morpheme (b.f.) that appears in compounds with two main semantic fields: one related to leather or animal hide (e.g., 皮革, 革制品), and another related to change, reform, or revolution (e.g., 革命, 革新, 改革). The existing English gloss "perilous" is not a standard meaning of this character — it likely refers to a rare or erroneous sense. In practice, you'll mostly encounter 革 as a component in formal or political vocabulary.