1570s, "that which defiles," from defile (v.) + -ment. From 1630s as "act of making foul; state of being unclean."
Entries linking to defilement
defile v.
c. 1400, "to desecrate, profane;" mid-15c., "to make foul or dirty," also "to rape, deflower," 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.1)).
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.
-ment
common suffix of Latin origin forming nouns, originally from French and representing Latin -mentum, which was added to verb stems to make nouns indicating the result or product of the action of the verb or the means or instrument of the action. In Vulgar Latin and Old French it came to be used as a formative in nouns of action. French inserts an -e- between the verbal root and the suffix (as in commenc-e-ment from commenc-er; with verbs in ir, -i- is inserted instead (as in sent-i-ment from sentir).
Used with English verb stems from 16c. (for example amazement, betterment, merriment, the last of which also illustrates the habit of turning -y to -i- before this suffix).
The stems to which -ment is normally appended are those of verbs; freaks like oddment & funniment should not be made a precedent of; they are themselves due to misconception of merriment, which is not from the adjective, but from an obsolete verb merry to rejoice. [Fowler]