I'll guess at this one. "Real" is an old form of "royal" = belonging to the king, and I think this usage grew out of the system of fiefdom/vasssalage. Kings owned the land under their control. They gave it to selected individuals who would support them with tax money and with troops to defend the land. So the holders of the land had their estates by virtue of the king's (roi) gift.

In common law, real estate refers to land and any other immovable property affixed to it, such as tress or buildings. The term real estate is often used interchangeably with the term real property, but the term real estate emphasizes the asset itself, and real property encompasses the legal issue of ownership. Although real estate is of paramount importance given its unique characteristics, precise economic statistics are difficult to obtain. Various estimates of the total value of all privately held real estate in the US are all in the trillions of dollars. Real estate is a tax-advantaged way to accumulate and hold wealth in the US. Important federal tax code provisions beneficial to real estate ownership such as the real estate mortgage interest deduction and the 1031 exchange rules for real estate investment property have no parallel in other asset classes. The etymology of real estate traces back to Spanish and Latin roots for the word regal, reflecting the medieval view that all European land was property of the monarchy. http://www.investorglossary.com/real-estate.htm

From Wikipedia... In law, the word real means relating to a thing (from Latin res, matter or thing), as distinguished from a person. Thus the law broadly distinguishes between real property (land and anything affixed to it) and personal property (everything else, e.g., clothing, furniture, money). The conceptual difference was between immovable property, which would transfer title along with the land, and movable property, which a person would retain title to. (The word is not derived from the notion of land having historically been "royal" property.[citation needed] The word royal — and its Spanish cognate real — come from the unrelated Latin word rex, meaning king.) In modern legal systems derived from English common law, classification of property as real or personal may vary somewhat according to jurisdiction or, even within jurisdictions, according to purpose, as in defining whether and how the property may be taxed..

real; from French royale, from Latin regalis, royal, regal, from combining form reg- (nominative rex), king, + adjective suffix -alis estate; from Latin status, condition, state In spite of the name, real estate has no connection with the concept of reality. It derives instead from the feudal principle that in a monarchy, all land was considered the property of the king. Thus originally the term real estate was equivalent to "royal estate", real originating from the French royale, as it was the French-speaking Normans who introduced feudalism to England in the 11th century and thus the English language; cognate to Spanish real. http://en.wiktionary.org/wiki/Real_estate In law, the word real means relating to a thing (from Latin res/rei, thing), as distinguished from a person. Thus the law broadly distinguishes between "real" property (land and anything affixed to it) and "personal" property (everything else, e.g., clothing, furniture, money). The conceptual difference was between immovable property, which would transfer title along with the land, and movable property, which a person would retain title to. (The word is not derived from the notion of land having historically been "royal" property. The word royal — and its Portuguese cognate real — come from the related Latin word rex-regis, meaning king.). http://en.wikipedia.org/wiki/Real_estate syn: real property. [Origin: 1705–15]