【Gentleman】 , 【patrician】 ,  【aristocrat】  are comparable when they denote a person of good or noble birth.

【Gentleman】 basically implies descent from good family, the right to bear a coat of arms, and social rank just below that of the noble and above that of the yeoman. The term has been widely extended in its application and has acquired connotations which have little or nothing to do directly with lineage or heraldic rights but suggest only such outward marks of good birth as elegance of person and of manners and a life of leisure.

【Patrician】 derives its implications from its historical applications but chiefly from its earliest reference to a Roman citizen who belonged to one of the original families of ancient Rome which, after the growth of the plebeian order, kept power and authority in their own hands. In reference to present-day persons the word suggests a distinguished ancestry, superior culture, and aloofness from what is common or vulgar; it is applied chiefly to descendants of established and influential families when they constitute a social caste, especially one marked by exclusiveness and pride in birth.

【Aristocrat】  carries fewer suggestions of inbred physical characteristics than  【gentleman】  or  【patrician】 , but it suggests a sympathy with the point of view common to them. In historical use it commonly implies an opposition to democrat and is applicable to a person who believes in government by superior persons or by the class which includes such persons; in more general use it is commonly applied to a person who by reason of birth, breeding, title, wealth, or outlook is accorded recognition as a member of the highest caste and especially to one who holds himself somewhat aloof from the ordinary forms and observances of social life.