The only free and comprehensive online etymological dictionary of the Spanish language
faltar (Verb) "to fault"
14th cent. From Latin faltare 'id.,' from fallere "to deceive" (see fallar) and -tare, a frequentive suffix.

The frequentive suffixes in Latin indicated repeated actions. Suffixes like these are akin to the English suffix -le, found in words like joust ~ jostle and mud ~ muddle. Suffix -tare belongs to a larger group of frequentive suffixes in Latin, -tare, -(s)sare, and -itare, all derived from the present tense of the ancient verb. See Sihler (2008) for further discussion.

For information on the Latin suffixes -titare and -sitare as found in Spanish, see cantar.