c. 1200, "of wide application, generic, affecting or involving all" (as opposed to special or specific), from Old French general (12c.) and directly from Latin generalis "relating to all, of a whole class, generic" (contrasted with specialis), from genus (genitive generis) "stock, kind" (from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups).
What is common is of frequent occurrence.
What is general admits of comparatively few exceptions: the general opinion (the opinion of the majority); the general welfare.
[J.H.A. Günther, "English Synonyms Explained & Illustrated," Groningen, Netherlands, 1904]
Used in forming titles from late 14c. with the sense "having general authority or jurisdiction, chief." Phrase in general "without exception, in one body; as a rule, generally, not specifically" is from late 14c. General rule, one applying to an art or science as a whole, is from c. 1400. General store attested by 1810, American English, in reference to the range of goods sold; a general hospital (1737) is one not restricted to one class of persons or type of disease.