The name Sinjin is of English origin, derived from the Old English name Sincyn, which is a diminutive form of the name Sincyn or Sincin. This name can be traced back to the 7th century in England and is believed to be derived from the Old English word "sinc," meaning "treasure" or "jewel."

One of the earliest recorded instances of the name Sinjin can be found in the Domesday Book, a historic record compiled in 1086 under the orders of William the Conqueror. The entry mentions a landowner named Sinjin de Hastings, who held land in Norfolk, England.

In the 12th century, a monk named Sinjin of Brixworth is recorded as having lived at the Augustinian priory in Brixworth, Northamptonshire. His writings on religious matters and philosophy have been preserved in various monastic archives.

During the Middle Ages, the name Sinjin was relatively uncommon but maintained a presence among the English nobility. One notable figure was Sir Sinjin Audley, a 14th-century knight who fought alongside Edward III in the Hundred Years' War against France.

In the 16th century, the name gained some popularity in literary circles. Sinjin Marlowe, a playwright and contemporary of William Shakespeare, is credited with several works, including the tragedy "The Tragical History of Doctor Faustus."

The name Sinjin also appears in historical records from the American colonies. Sinjin Brewster, born in 1630, was among the early Puritan settlers in Massachusetts and is recorded as being a prominent figure in the establishment of the town of Duxbury.

As the centuries passed, the name Sinjin became less common, but it has been adopted by a few notable individuals throughout history. Sinjin Smith, an American professional tennis player born in 1954, achieved fame in the 1980s and won numerous doubles titles on the ATP Tour.