also: イニシアル
noun
initials; first letter of a name
Refers to the first letter(s) of a person's name, often used in signatures, monograms, or when abbreviating names.
書類にイニシャルを記入してください。
Please write your initials on the document.
彼のイニシャルはT.S.だ。
His initials are T.S.
noun, noun which may take the genitive case particle 'no'
Used as a noun or adjectivally with の to mean 'first' or 'initial' in a sequence, such as the first letter of a word or the first stage of something.
単語のイニシャルの文字を大文字にしてください。
Please capitalize the initial letter of the word.
イニシャルの段階では、まだ計画は確定していない。
At the initial stage, the plan hasn't been finalized yet.