initial|initials

Paul M. Reynolds拒绝说出首字母'M'代表什么。

Paul M. Reynolds refused to say what the ___initial "M" stood for.

他们把他们的首字母刻在了一棵树上。

They carved their ___initials into a tree.

他在页面底部写下了他的首字母缩写P.M.R.

He wrote his ___initials, P.M.R., at the bottom of the page.