Huh, I think of "Sgoinneil" as "Terrific." A few minutes on Learn Gaelic Dictionary and Am Faclair Beag, leaves me not finding this word under either Terrific or Brilliant. on the other hand, the closest thing AFB gives to the usage I know is "Cool, Groovy (coll.)" So updating that to modern English, "Brilliant" is probably about right. Leave as is.