beware
v.to be careful or look out for something dangerous. You often see this on signs to warn you about a risk.
v.to be cautious or on one's guard against potential danger or harm. Primarily used in the imperative or as an infinitive; lacks a full range of inflected forms like a past tense.
“Beware of the dog when you enter the yard.”
“Hikers should beware of falling rocks when walking along the base of the cliffs after a heavy rain.”
“While the investment opportunity appears lucrative on the surface, seasoned traders warn that one must beware of hidden fees that can quickly erode any potential profit margins.”
Beware is a defective verb and cannot be used in the past tense; use 'was wary of' or 'avoided' instead.
“While the personal touch may work in OOOs if your team culture is informal, beware that humour doesn't always land well over email.”
From Middle English bewar, be war, be ware, forms of Middle English ben ware (“to be on one's guard, be vigilant”, literally “be ware”), equivalent to be + ware or be + aware. Compare Old English bewarian.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.