A modest person is humble, someone who is free from egotism, vanity, and boastfulness. A modest individual is moderate in his behavior and speech."Lincoln was a great but modest man." "Mrs. Morgan is a self-respecting, modest woman." A shy person is timid, easily frightened, and bashful. A shy girl wishes to escape notice and avoids close association with others: "Beth was once a shy, retiring girl who blushed easily." A shy person is diffident; a modest person is unassuming.
Dictionary of problem words and expressions. Harry Shaw. 1975.