Digital Companion to C. S. Peirce
1897 | The Logic of Relatives | CP 3.465

In a complete proposition there are no blanks. It may be called a medad, or medadic relative

1898 | Cambridge Lectures on Reasoning and the Logic of Things: Detached Ideas continued and the Dispute between Nominalists and Realists | RLT 154; NEM 4:338

I distinguish verbs according to the numbers of their subject blanks, as medads, monads, dyads, triads, etc. A medad, or impersonal verb, is a complete assertion, like “It rains,” “you are a good girl.”

1903 | Lectures on Pragmatism [R] | PPM 235; EP 2:221

A rhema containing one blank I call a monad, that containing two a dyad, etc. An entire proposition I term a medad, from μηδέν.

1903 [c.] | On Logical Graphs | CP 4.354

…let a number of the proper designations of individual subjects be omitted, so that the assertion becomes a mere blank form for an assertion which can be reconverted into an assertion by filling all the blanks with proper names. I term such a blank form a rheme. If the number of blanks it contains is zero, it may nevertheless be regarded as a rheme, and under this aspect, I term it a medad. A medad is, therefore, merely an assertion regarded in a certain way, namely as subject to the inquiry, How many blanks has it?

1903 [c.] | Logical Tracts. No. 2. On Existential Graphs, Euler's Diagrams, and Logical Algebra | CP 4.438

A rhema with no blank is called a medad, and is a complete proposition.

1906 [c.] | Prolegomena to an Apology for Pragmaticism | CP 1.292

In the present application, a medad must mean an indecomposable idea altogether severed logically from every other; a monad will mean an element which, except that it is thought as applying to some subject, has no other characters than those which are complete in it without any reference to anything else; a dyad will be an elementary idea of something that would possess such characters as it does possess relatively to something else but regardless of any third object of any category; a triad would be an elementary idea of something which should be such as it were relatively to two others in different ways, but regardless of any fourth; and so on. Some of these, I repeat, are plainly impossible. A medad would be a flash of mental “heat-lightning” absolutely instantaneous, thunderless, unremembered, and altogether without effect.