What is "to look daggers"

Look \Look\, v. t.

1. To look at; to turn the eyes toward.

2. To seek; to search for. [Obs.]

   Looking my love, I go from place to place.
   --Spenser.

3. To expect. [Obs.]
   --Shak.

4. To influence, overawe, or subdue by looks or presence as, to look down opposition.

   A spirit fit to start into an empire, And look the world to law.
   --Dryden.

5. To express or manifest by a look.

   Soft eyes looked love to eyes which spake again.
   --Byron.

   To look daggers. See under Dagger.

   To look in the face, to face or meet with boldness or confidence; hence, sometimes, to meet for combat.

   To look out, to seek for; to search out; as, prudent persons look out associates of good reputation.

Dagger \Dag"ger\ (-g[~e]r), n. [Cf. OE. daggen to pierce, F. daguer. See Dag a dagger.]

1. A short weapon used for stabbing. This is the general term: cf. Poniard, Stiletto, Bowie knife, Dirk, Misericorde, Anlace.

2. (Print.) A mark of reference in the form of a dagger [[dagger]]. It is the second in order when more than one reference occurs on a page; -- called also obelisk.

   Dagger moth (Zo["o]l.), any moth of the genus Apatalea. The larv[ae] are often destructive to the foliage of fruit trees, etc.

   Dagger of lath, the wooden weapon given to the Vice in the old Moralities.
   --Shak.

   Double dagger, a mark of reference [[dag]] which comes next in order after the dagger.

   To look daggers, or To speak daggers, to look or speak fiercely or reproachfully.