From Longman Dictionary of Contemporary Englishdaggerdag‧ger /ˈdæɡə $ -ər/ noun [countable] 1 
PMWa short pointed knife used as a weapon2 → look daggers at somebody3 → be at daggers drawn → cloak-and-dagger
PMWa short pointed knife used as a weapon2 → look daggers at somebody3 → be at daggers drawn → cloak-and-daggerExamples from the Corpus
dagger• Even though she'd expected it, that smile twisted in Shannon's heart like a dagger.• Caterina takes a dagger from the gallery artifact collection and goes to meet him.• The two combatants were armed with spears and shields, and each man had sword and dagger at his belt.• It was rather like having a heated dagger thrust into the eyeball and twisted, then caustic soda rubbed in the wound.• Their relationship is not free and easy but at least Red is no longer looking daggers at her.• I jumped to one side, and the dagger went deep into my shoulder.• As the dagger went in, the bush turned grey and all its thorns went pale and soft.Origin dagger (1300-1400) Perhaps from dag “to push a knife into” ((14-18 centuries)) 