forewarn

Universal Words verb [oftenpassive] ~ sb (of sth) (written) to warn sb about sth bad or unpleasant before it happens: [VN] The commander had been forewarned of the attack. [also VNthat] forewarning noun [U,C] IDIOMS forewarned is forearmed (saying) if you know about problems, dangers, etc. before they happen, you can be better prepared for them