It comes from the word hypothesis.
The easiest way to explain it is to use it in a sentence.
"What is the air speed velocity of a swallow carrying a coconut?"
"Swallows do not carry coconuts."
"Ok well, hypothetically, what would it be if they did carry coconuts?"
"But" can mean "hypothetically" or "in contradiction," and be replaced with "however" or "actually."
hypothetically
It's possible to do anything hypothetically.
Heretical Alphabetical Theoretical
Hypothetically is a term used to propose a fictional situation. For example, I could say, "If I hypothetically won a million dollars, I would buy a jet." This sentence shows the outcome of a fictional situation.
Hypothetically is basically posing a "What-if" Scenario. People ask a question hypothetically when they're not saying a certain path of events will happen, but they want to consider the possibility.
Hypothetically anything is possible but not probable.
The cast of Hypothetically - 2008 includes: Mike Lucero as Trey
Hypothetically
The cast of Hypothetically - 2013 includes: Joe Forbrich as Eugene Vincent Pastore as Gene Mickey Sumner as Colleen
Hypothetically, it's a continent.
Nibiru is a hypothetical planet and will hypothetically hit Earth in 2012 causing hypothetically disastrous results. With no doubt, loads of hypothetical law suites.