Quiz: Remember the definition of mal de mer?
past participle adjective from skill (v.) "to have personal and practical knowledge" (c.1200), from Old Norse skilja "separate, part, divide; break off, break up; part company, take leave; discern, distinguish; understand, find out; decide, settle," from the source of skill (n.).
late 12c., "power of discernment," from Old Norse skil "distinction, ability to make out, discernment, adjustment," related to skilja (v.) "to separate; discern, understand," from Proto-Germanic *skaljo- "divide, separate" (cf. Swedish skäl "reason," Danish skjel "a separation, boundary, limit," Middle Low German schillen "to differ," Middle Low German, Middle Dutch schele "separation, discrimination;" see shell (n.)). Sense of "ability, cleverness" first recorded early 13c.