(one's) initials; first letter (of a name, sentence, etc.)
initial; first
結婚指輪にイニシャルを刻んだ。
We had our initials engraved on the wedding rings.
証人のプライバシー保護のため、イニシャル表記にした。
To protect the witness's privacy, they were referred to by their initials.
誕生日にイニシャル入りの革のブリーフケースをもらった。
For my birthday, I received a leather briefcase with my initials on it.