1.  Generally considered someone following a particular spiritual path, it specifically means person who assists in a ritual.

2.  (Magick – Ceremonial) “Morvan’s duty was to keep this brazier fed and at an even height temperature, also to serve him generally as an acolyte serves a priest. She had, however, a much more important part to play in the actual ritual, which was to fix her mind unwaveringly on the work, to do her best to make it fluid, so that in welding it with his as it were, he derived added strength. For this concentration of the will upon the object of the ritual there must be no means of distraction. Everything used must be with this object in view, so everything used brings to the brain of the Magus, the reason of the work. Therefore was Thur clad in the symbolically pure, clean white linen robe, signifying light, strength and purity, also this is important, bearing no color or pattern that could distract the mind of the wearer or his acolyte. For the same reason the girl was nude, this signified purity unsullied, and the natural magnetism in the human body could flow unhindered to the support of the Magus.” Pg 252 High Magic’s Aid, by "Scire" (Gerald Gardner), 1949, Michale Houghton, London