‘Defraud’ is clearly another euphemism. The Scripture is very careful about how it speaks of these things, and we ought to preserve the same modesty. The modern habit to bringing everything out into the open and talking publicly about the most private things is foolishness. Perhaps the world does this to suppress its own sense of shame about so much of its conduct.
Paul rejects any suggestion that marital relations should be avoided, as if they were unclean. By using the strong word ‘defraud’, he says that on the contrary, there is an obligation of one to the other. Literally the word means to obtain something by deception. In this case, what is obtained is a release from physical marital relations. Any exception to this must be temporary only.