An uncertainty, possibility, condition, doubt etc.
Supposing that, assuming that, in the circumstances that; used to introduce a condition or choice.
In the event that a statement is true (a programming statement that acts in a similar manner).
Supposing that; used with past or past perfect subjunctive indicating that the condition is closed.
Supposing that; given that; supposing it is the case that.
Although; used to introduce a concession.
(sometimes proscribed) Whether; used to introduce a noun clause, an indirect question, that functions as the direct object of certain verbs.
(usually hyperbolic) Even if; even in the circumstances that.
Introducing a relevance conditional.