defile (v.)youdaoicibaDictYouDict
c. 1400, "to desecrate, profane;" mid-15c., "to make foul or dirty," alteration of earlier defoulen, from Old French defouler "trample down, violate," also "ill-treat, dishonor," from de- "down" (see de-) + foler "to tread," from Latin fullo "person who cleans and thickens cloth by stamping on it" (see foil (v.)).

The alteration (or re-formation) in English is from influence of Middle English filen (v.) "to render foul; make unclean or impure," literal and figurative, from Old English fylen (trans.), related to Old English fulian (intrans.) "to become foul, rot," from the source of foul (adj.). Compare befoul, which also had a parallel form befilen. Related: Defiled; defiling.
untouchable (adj.)youdaoicibaDictYouDict
1560s, "immaterial," from un- (1) "not" + touchable (see touch (v.)). Meaning "that legally cannot be interfered with" is recorded from 1734. Meaning "too loathsome or defiling to be touched" is recorded from 1873. The noun, in reference to a hereditary low caste of India, is attested from 1909; the term and the restrictions were made illegal in India in 1947.