Of course, JWs will define "apostate" any way they want to; it becomes a label that scares many from pursuing freedom of thought.
Webster's defines it as One who has forsaken the faith, principles or party, to which he before adhered, esp. one who has forsaken his religion for another; a pervert, a renegade. Or, as one who, after having received sacred orders, renounces his clerical profession.
JWs would do well to consider if their current course is, in fact apostacy (many came from other faiths they once adhered to, right?) and if they are prepared for the responsibility that includes. (I'm not one bit serious here!)
They've got it all worked out, huh. No wonder some people actually go back and get reinstated.