We need to popularize “anti-” as an alternative prefix to “a-”
In vernacular English, the “a-” prefix gets used with somewhat broad and ambiguous meanings. It might indicate a neutral or indifferent position or the lack of a position or action. It might also or instead indicate an actively opposed position or action. These two meanings are easy to confuse. When a single word is used to mean both or either of them, lack of clarification can lead to significant miscommunications.
Atheist can mean that you don't hold any specific theistic/religious belief. It could also mean that you explicitly believe there is no supernatural higher power. Sometimes “agnostic” is used for the former meaning to clarify this distinction, but that usage is less widespread.
Apolitical can mean that you don't engage with the political process, or that you aren't aligned with existing political parties, or that you are actively opposed to the current (or any) political system. These all have very different implications for what actions you might support or take with regard to the political process.
Asexual can mean that you don't experience sexual desire and/or are indifferent to seeing or participating in sexual activities. It could instead mean that you are mildly to extremely unhappy with exposure to and/or participation in sexual activity. The appropriate responses from a [prospective] romantic or intimate partner to these two different meanings are wildly different.
There are also some lesser examples adjacent to this pattern, such as “anonymous” which might be an incidental or temporary or local state of affairs or an intentional choice and permanent goal. As the effect of the distinction shrinks, so does the need for clarification.
I propose here that our ability to communicate effectively about these topics would benefit from separating these meanings into “a-” for indifference and “anti-” for opposition, in precisely the same way that they are already separated for “apathy” vs “antipathy”.
Someone who explicitly disclaims the existence of god is antitheist, not just atheist.
Someone who explicitly opposes the political process is antipolitical, not just apolitical.
Someone who is unhappy when exposed to sex is antisexual, not just asexual.
This isn't a new idea. These words and meanings and usages already exist, but they are not popular. We should change that. I've made the distinction occasionally in the past, but I intend to approach this more directly. You can expect to hear “Do you mean antiwhatever, or are you really just indifferent?” from me more in the future, especially in rationalist and other communities with a focus on effective communication.