What's a sqian achlais? It translates as “arm pit dagger”, and was worn concealed under the arm. Where the sgian dubh was almost certainly a utility knife, the sgian achlais was truly a concealed weapon. How exactly it was concealed is not well documented — it's up to you to figure it out for yourself. Probably slung with a leather strap or cord. Possible just tucked into the folds of a great kilt, or inside a jacket.