dagger

at daggers drawn in a state of bitter enmity.

☞ The image here is of the drawing of daggers as the final stage in a confrontation before actual fighting breaks out. Although recorded in 1668, the expression only became common from the early 19th century onwards.

look daggers at glare angrily or venomously at.

☞ The expression speak daggers is also found, and is used by Shakespeare's Hamlet in the scene in which he reproaches his mother.