1. [n]  position 14 in a countable series of things
2. [adj]  coming next after the thirteenth in position

FOURTEENTH is a 10 letter word that starts with F.

1. \Four"teenth`\, a. [Cf. OE. fourtende, fourtethe, AS.
   fe['o]werteo[eth]a.]
   1. Next in order after the thirteenth; as, the fourteenth day
      of the month.
   
   2. Making or constituting one of fourteen equal parts into
      which anything may be derived.
   
   

2. \Four"teenth`\, n.
   1. One of fourteen equal parts into which one whole may be
      divided; the quotient of a unit divided by fourteen; one
      next after the thirteenth.
   
   2. (Mus.) The octave of the seventh.