shamefaced
adj.
"modest, bashful," 1550s, folk etymology alteration of shamefast, from Old English scamfæst "bashful," literally "restrained by shame," or else "firm in modesty," from shame, n. + -fæst, adjectival suffix (see fast, adj.). Related: Shamefacedly; shamefacedness.
shamefaced, -fast. It is true that the second is the original form, that -faced is due to a mistake, & that the notion attached to the word is necessarily affected in some slight degree by the change. But those who, in the flush of this discovery, would revert to -fast in ordinary use are rightly rewarded with the name of pedants .... [Fowler]