(g soft) means having the manners of genteel persons —i.e. persons of family, called gens in Latin.
“We must be gentle, now we are gentlemen.” -
“Here Hans Sachs, the cobbler poet, laureate of the gentle craft,
Wisest of the Twelve Wise Masters, in huge folios sang and laughed.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Gentle from Infoplease: