Of is defined as to indicate ownership or distance from something.(preposition)
See of in Webster's New World College Dictionary
Origin: ME < OE, unstressed var. of af, æf, away (from); akin to Ger ab < IE base *apo-, from, away from > L ab (see ab-), Gr apo-
See of in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Old English; see apo- in Indo-European roots. Usage Note: Grammarians have sometimes objected to the so-called double genitive construction, as in a friend of my father's; a book of mine. But the construction has been used in English since the 14th century and serves a useful purpose. It can help sort out ambiguous phrases like Bob's photograph, which could refer either to a photograph of Bob (that is, revealing Bob's image) or to one in Bob's possession. A photograph of Bob's can only be a photo that Bob has in his possession, which may or may not show Bob's image. Moreover, in some sentences the double genitive offers the only way to express what is meant. There is no substitute for it in a sentence such as That's the only friend of yours that I've ever met, since sentences such as That's your only friend that I've ever met and That's your only friend, whom I've ever met are awkward or inaccurate.Our Living Language Some speakers of vernacular English varieties, particularly in isolated or mountainous regions of the southern United States, use phrases such as of a night or of an evening in place of Standard English at night or in the evening, as in We'd go hunting of an evening. This of construction is used only when referring to a repeated action—where Standard English uses nights, evenings, and the like, as in We'd go hunting nights. It is not used for single actions, as in She returned at night. • Interestingly, these of and -s constructions are related. This -s construction, which dates back to the Old English period (c. 449-1100), does not signify a plurality but is similar to the so-called genitive suffix -s, which often indicates possession, as in the king's throne. Just as this example can also be phrased as the throne of the king, nights can be reformulated as of a night. This reformulation has been possible since the Middle English period (c. 1100-1500). Sometimes the original -s ending remains in the of construction, as in We'd walk to the store of evenings, but usually it is omitted. Using of with adverbial time phrases has not always been confined to vernacular speech, as is evidenced by its occurrence in sources from the Wycliffite Bible (1382) to Theodore Dreiser's 1911 novel Jennie Gerhardt: “There was a place out in one corner of the veranda where he liked to sit of a spring or summer evening.” • Using such of constructions reflects a long-standing tendency for English speakers to eliminate the case endings that were once attached to nouns to indicate their role as subject, object, or possessor. Nowadays, word order and the use of prepositional phrases usually determine a noun or noun phrase's role. Despite the trend to replace genitive -s with of phrases, marking adverbial phrases of time with of is fading out of American vernacular usage, probably because one can form these phrases without -s, as in at night. See Note at Smith Island.
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