Source : Webster's Revised Unabridged Dictionary (1913)

Foal \Foal\, n. [OE. fole, AS. fola; akin to OHG. folo, G.
   fohlen, Goth. fula, Icel. foli, Sw Lf?le, Gr. ?, L. pullus a
   young animal. Cf. {Filly}, {Poultry}, {Pullet}.] (Zo["o].)
   The young of any animal of the Horse family {(Equid[ae])}; a
   colt; a filly.

   {Foal teeth} (Zo["o]l.), the first set of teeth of a horse.
      

   {In foal}, {With foal}, being with young; pregnant; -- said
      of a mare or she ass.

Foal \Foal\, v.t. [imp. & p. p. {Foaled}; p. pr. & vb. n.
   {Foaling}.]
   To bring forth (a colt); -- said of a mare or a she ass.

Foal \Foal\, v.i.
   To bring forth young, as an animal of the horse kind.

Source : WordNet®

foal
     n : a young horse
     v : give birth to a foal; "the mare foaled"