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Meaning of if
The primary meaning of the word "if" is to introduce a condition or hypothesis.
Etymology of if
The word "if" originates from Old English "gif", which is also the source of the Modern English word "give", 
 It is related to the Old Norse word "ef" and the German word "ob", both of which are also used to introduce conditions or hypotheses, 
 The word "if" has been used in the English language since the 9th century to introduce conditions, hypotheses, and uncertain situations.
Synonyms
                                                although
                                                                        assuming
                                                                        in case
                                                                        provided
                                                                        providing
                                                                        suppose
                                                                        supposing
                                                                        granting
                                                                        given
                                                                        considering
                                                                        on condition
                                                                        unless
                                                                        except
                                                                        should
                                                                        in the event
                                                                        provided that
                                                                        if so
                                                                        if not
                                                                        just in case
                                                                        lest
                                                                        unless
                                                                        inasmuch
                                                                        whereas
                                                                        while
                                                                        whereas
                                                                        even if
                                                                        even though
                                                                        just in case
                                                                        on the off chance
                                                                        pending
                                                                        on condition that
                                                                        in the event that
                                                                        supposably
                                                                        conditionally
                                                                        hypothetically
                                                                        theoretically
                                                            
            Definitions
- Used to introduce a condition or hypothesis,
 - To express a possible or uncertain situation,
 - To introduce a clause that describes a condition or circumstance,
 - To indicate a doubt or uncertainty about something,
 - Used in a clause that describes an uncertain or possible situation.
 
Usage Examples
- I will go to the party if you go with me,
 - If it rains, we will stay indoors,
 - If I won the lottery, I would buy a house,
 - She will only go to the movie if her favorite actor is in it,
 - If you don't study, you will fail the exam.