initial vs simplex

initial

noun
  • The first letter of a word or a name. 

  • A distinguished initial letter of a chapter or section of a document. 

  • onset, part of a syllable that precedes the syllable nucleus in phonetics and phonology. 

  • In plural, the first letter of each word of a person's full name considered as a unit. 

adj
  • Spatially first, placed at the beginning, in the first position; especially said of the first letter of a word. 

  • Chronologically first, early; of or pertaining to the beginning, cause or origin. 

verb
  • To sign one's initial(s), as an abbreviated signature. 

simplex

noun
  • A monomorphemic word, one without affixes. 

  • An analogue in a space of arbitrary dimensionality of the triangle or tetrahedron; the convex hull of n+1 linearly independent points in n-dimensional space; in other words, the triangle, tetrahedron etc., generalized to an arbitrary number of dimensions. 

adj
  • Single, simple; not complex. 

  • Unidirectional. 

How often have the words initial and simplex occurred in a corpus of books? (source: Google Ngram Viewer )