Magnus is Latin for great, a name once given directly to rulers and later adopted more broadly without losing its scale. It states its meaning outright rather than through symbol or story -- greatness as a plain description, left for the bearer to grow into.
The virtues of the planets are received by the Sun, when he is posited either in the ascendant or midheaven, in conjunction of them. The Moon in the night-time receives them also, if in the aforesaid places, she be joined to them. - William Lilly (1602.-1681.)