conditional conjunction
Definition - A conjunction that is used to express a condition — e.g. if, since, and unless.

Example -
If he goes, I will stay.
(In the above, if is the conjunction that introduces the condition if he goes.)

Oxford English Dictionary -
The term's first citation is from 1786:
"Those words which are called conditional conjunctions, are to be accounted for in all languages … as I have accounted for If and An."
(H. Tooke Purley 56)

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