defect
n.
early 15c., from Middle French defect and directly from Latin defectus "failure, revolt, falling away," noun use of past participle of deficere "to fail, desert" (see deficient).
v.
1570s, from Latin defectus, past participle of deficere "to fail, desert" (see defect, n.). Related: Defected; defecting.
〔李〕[de-=away, down 离，下降；fect=to do 做→“to do away with one's duty, etc.离开所做之事”→]Ⅰv. desert开小差；背叛