The root is advertently. That means “knowingly”. Fair enough. The root of advertently is advertent. That means “attention”. Hmmm … quite close. The root of advertent is advert, which means “advertising”. Okay, I am missing something here. What does advertising have to do with advertently? Are these the real root words?
Why do you think inadvertently means unknowingly? It doesn’t. It means, in the OED’s definition, ‘without due attention or thought; inattentively, heedlessly, carelessly; hence, unintentionally.’
The root meaning of words derived from Latin advertere is ‘turn or direct towards’. Advertent means ‘intentional, deliberate; conscious’, because in being advertent we pay attention to something, that is, we turn our minds towards it. An advertisement turns our direction towards the product or service that the advertiser is promoting.