Английский Этимологический словарь - fault (n.)

- c.1280, from O.Fr. faute "lack, deficiency," from V.L. *fallita "a shortcoming, falling," n. use of fem. pp., from L. falsus, pp. of fallere "deceive, disappoint" (see false). The -l- was restored 1400s, probably in imitation of L., but was not pronounced till 18c. Sense of "moral culpability" is late 14c.; the use in tennis (1599) is closer to the etymological sense.