horn  
noun uk/hɔːn/ us/hɔːrn/
  (ANIMAL)     
 C1 [ C or U ]角;角质 
a hard, pointed, often curved part that grows from the top of the head of some animals, or the hard substance of which a horn is made
 - More examples
- The male deer grows large branching horns called antlers.
- The bull lowered its horns and charged straight at him.
  (VEHICLE)      
 B2 [ C ](车辆的)喇叭 
a device on a vehicle that is used to make a loud noise as a warning or signal to other people
  The driver blew/sounded (informal honked) her horn. 那个司机按了喇叭。 
 See also: foghorn
   (MUSIC)     
C2 [ C ](乐器)号 
a curved metal musical instrument that is narrow at the end you blow into and much wider at the other end
 Idioms     
be on the horns of a dilemmaidiom  左右为难,进退维谷
to be unable to decide which of two things to do because either could have bad results
 draw/pull in your hornsidiom  行为收敛;(尤指)减少开支
to behave in a more careful way than you did before, especially by spending less money
  He'll have to draw in his horns now he's lost his job. 由于丢掉了工作他将不得不减少开支。