Obstruction
Hindrance, Preventing
noun, verbal noun
If you thwart and stop something, you are an obstruction or hindrance.
阻止 is a relatively formal word that means preventing something from happening, often by actively resisting rather than just stopping something passively.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
その証人が法廷で証言するのを、何としてでも阻止するんだ。
Do whatever it takes to prevent that witness from testifying in court.