A knife in a dream can point to a threat you sense but haven't named, or to a truth that feels sharp enough to cut through pretense. Holding the knife yourself often reflects a decision to cut ties with something, while facing one aimed at you may point to feeling exposed or attacked.
When the Moon is in a fixed sign, neither cut out, or put on any new garments, chiefly in Leo, for 'tis extreme dangerous: 'tis the same if she be in conjunction or opposition of the Sun, or impedited of the infortunes. - William Lilly (1602.-1681.)