The prefix a can have various meanings, depending on the context. It can mean not or without, as in the word 'amoral' (without morals) or 'asymmetrical' (not symmetrical). It can also mean 'toward' or 'in the direction of,' as in the word 'approach' (to come closer to something). In some cases, a is simply a variant of the prefix 'an,' which means not or without, as in 'atheist' (one who does not believe in God) or 'anaemic' (without vigour or energy).