Could you please tell me the meaning of "sterner" in this passage extracted from Chapter 4 of The Great Gatsby?
Benny McClenahan arrived always with four girls. They were never quite the same ones in physical person, but they were so identical one with another that it inevitably seemed they had been there before. I have forgotten their names—Jaqueline, I think, or else Consuela, or Gloria or Judy or June, and their last names were either the melodious names of flowers and months or the sterner ones of the great American capitalists whose cousins, if pressed, they would confess themselves to be.
In Chapter Four of The Great Gatsby, Nick Carraway takes it upon himself to record the names of Gatsby's guests upon the blank spaces in a timetable; these people are among "the world and its mistress" as Fitzgerald writes in his opening sentence. Nick records the names of upper-class families, and those of "theatrical families." But, the girls who are not starlets with names "like flowers," belonged to those of "sterner" names. Such names as Rockefeller, Morgan, For, Mellon, Vanderbilt, Guggenheim, Astor, Baker, and Dupont are surpressed in conversation. These are the "sterner ones" of which Fitzgerald makes mention, for many are aristocratic names or ones made "sterner" by the patriarch who has associated himself with only that which is profitable and respectable in his dealings--the names of the "Gilded Age" whose families are dynasties.
Thus, the girls who only give their first names, and not their "sterner" surnames wish to maintain a certain anonymity since they may be engaging in illicit affairs, or, at the least, are not with the proper people. Other guests, whose names Nick has recorded are
...the Chromes and the Backhyssons and the Dennickers and Russel Betty and the Corrigans and the Kellehers and the Dewars and the Scully and S.W.Belcher and the Smirkes and the young Quinns, divorced now, .....
These are the names that are not "sterner"; these are names of those who conduct themselves amorally.
Ok, but what is the litteral meaning of "stern" here? which synonymous could be employed?