1
first letter of a word;capital letter (at the start of a word or sentence)
頭文字のＮＴＴは何を表していますか。
What do the initials NTT stand for?
2
initials (of one's name)
「あなたはたしか・・・えーと、えーと・・・も」「頭文字から間違っとるわい！！」
"Let's see, you're ... er, um ... M-" "You're wrong from the first letter!!"