Circumlocution is an ambiguous or roundabout figure of speech. For example, instead of saying ‘Throw that in the trash bin’, one might say, ‘Throw that it in the oblong somewhat cone shaped silver container with a beveled lip'.
It seems to indicate an intentional avoidance of using the simple word and indicating that the Jewish Sabbath is no longer a valid institution after Christ died.
The argument of Matthew's use of circumlocution does not have clear intra-textural support, however as all understand Matthew to be focusing his account with more attention to its relationship to Jewish faith then the other gospels, the ideas is plausible. John 19:31 and Mark 15:42 use similar language in describing the passover day, but only Matthew seems to skip the obvious word. It seems hard to imagine that a Jewish audience, Matthew's audience, would not notice it missing.