because:  Because originated in the phrase by cause, which was directly modelled on French par cause. At first it was always followed by of or by a subordinate clause introduced by that or why: ‘The Holy Ghost was not yet given; because that Jesus was not yet glorified’, St John’s Gospel, 7:39, 1611. But already by the end of the 14th century that and why were beginning to be omitted, leaving because to function as a conjunction, a move which would perhaps have exercised contemporary linguistic purists as much as ‘The reason is because …’ does today. The abbreviated form ’cause first appears in print in the 16th century. => cause
c. 1300, bi cause "by cause," modeled on French par cause. Originally a phrase, often followed by a subordinate clause introduced by that or why. One word from c. 1400. As an adverb from late 14c. Clipped form cause attested in writing by mid-15c.