This is the 250th most frequent Chinese word.
信
"信" means "trust," "faith," "letter," or "message."
In this sentence, the word "信" refers to a written letter or message.
他给我写了一封信。
He wrote me a letter.
Here, "信" is used as a verb meaning to believe or trust.
你的话我不信。
I don't believe what you said.
In this context, "信" relates to faith or belief, as part of the word "信仰" (faith).