нача́льный

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

• That was my initial concern, too.

  Tatoeba · CK · CC BY 2.0 FR

нача́льный

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

The first letter of a word or a name, especially of a person's full name (their initials)

A distinguished initial letter of a chapter or section of a documentредкое

onset, part of a syllable that precedes the syllable nucleus in phonetics and phonologyредкое