guarantee, security, assurance, pledge, warranty
Example sentences
彼の性格については保証します。よく彼のことをしっていますから。
I'll answer for his character. I know him very well.
彼のことは長い間知っていますから、彼が正直であることは保証します。
I can answer for his honesty, since I have known him for a long time.
彼が来週には帰るという保証はない。
There is no guarantee that he'll be back next week.