Abarim Publications' online Biblical Greek Dictionary
The preposition απο (apo) can often be translated with "from" or "out of" but marks more than simply origin, as would the preposition εκ (ek). In stead απο (apo) emphasizes the former relationship of elements that had always existed independently but joined within a realm of origin, and the present separation from both that realm and the other element(s).
This difficult concept lives on in English words such as apostasy (literally a separation from that which stands), apothecary (literally a place where select items are put away) and of course apostle (literally an emissary, or someone appointed out of someone else).
Our preposition απο (apo) may describe leaving a place or community, but its use suggests that this separation comes with feelings such as grief or relief. It may likewise describe the removal of certain items from a place or person, which may bring our word close to the idea of cleansing. But it may also describe a removal of a person from the favor of someone else, or God.
Our word may demonstrate the beginning of an era or period relative to a previous situation from whence came the present, or even the very source from which something or some situation flowed. It may, as such, also describe a modus operandi or code of conduct or other instrument or agent.