Definition of "initial"

initial

/ɪˈnɪʃəl/

adjective
not comparable
1. Chronologically first, early; of or pertaining to the beginning, cause or origin.
  Quotations
  Meanwhile Nanny Broome was recovering from her initial panic and seemed anxious to make up for any kudos she might have lost, by exerting her personality to the utmost. She took the policeman's helmet and placed it on a chair, and unfolded his tunic to shake it and fold it up again for him.
  1963, Margery Allingham, chapter 19, in The China Governess‎
  While the first part to Manchester is level after the initial climb out of Liverpool, the section over the Pennines between Manchester and Leeds is very difficult, with steep gradients as well as many slowings over junctions and curves.
  2021 January 13, David Clough, “Trans-Pennine transport transformers”, in RAIL, issue 922, page 58
2. Spatially first, placed at the beginning, in the first position; especially said of the first letter of a word.
  Quotations
  Thus, when he drew up instructions in lawyer language, he expressed the important words by an initial, a medial, or a final consonant, and made scratches for all the words between; his clerks, however, understood him very well.
  1892, Walter Besant, “Prologue: Who is Edmund Gray?”, in The Ivory Gate […], New York, N.Y.: Harper & Brothers, […]
noun
plural initials
1. The first letter of a word or a name.
2. In plural, the first letter of each word of a person's full name considered as a unit.
3. (typography, calligraphy) A distinguished initial letter of a chapter or section of a document.
4. (phonology) onset, part of a syllable that precedes the syllable nucleus in phonetics and phonology.
verb
third-person singular simple present initials, present participle initialing or initialling, simple past and past participle initialed or initialled
1. (transitive) To sign one's initial(s), as an abbreviated signature.