Delta is the fourth letter of the Coptic alphabet and carries the numeral value four. Like gamma before it and zeta after it, delta is one of the Greek letters that Coptic kept although Egyptian had little use for the sound. It appears chiefly in Greek loanwords, in scriptural names such as David and Damian, and in Greek liturgical formulae preserved inside Coptic services, where a whole phrase may be left in its original language. Coptic grammars accordingly treat the presence of delta, along with a few other letters, as circumstantial evidence that a word has been borrowed rather than inherited, a rule of thumb useful to a student and never quite absolute. The letter keeps its place in the numeral series without qualification. Every Greek derived letter in the Coptic alphabet holds the value it held in Greek, and a Coptic scribe writing a date, a chapter head or the number of a quire used delta for four exactly as a Greek scribe did.
The numerals also generate their own small conventions in Coptic manuscripts, including overlines to mark a letter as a figure rather than a sound, so that the same shape can be read two ways without ambiguity on a crowded page. Delta is also one of the letters whose Coptic name and Greek name never diverged. Several Coptic letters acquired names of their own, ei for the Greek epsilon among them, and all seven of the letters brought in from Demotic carry Egyptian names; delta simply kept the Greek word, as gamma and zeta did. The alphabet chart used in Coptic Orthodox church schools today therefore mixes three kinds of name in a single unbroken column, Greek names kept, Greek names altered, and Egyptian names for the Egyptian additions, with nothing on the page to show which is which.