FETTLE is a 6 letter word that starts with F.

1. \Fet"tle\, v. t. [OE. & Prov. E., to fettle (in sense 1),
   fettle, n., order, repair, preparation, dress; prob. akin to
   E. fit. See {Fit}, a.]
   1. To repair; to prepare; to put in order. [Prov. Eng.]
      --Carlyle.
   
   2. (Metal.) To cover or line with a mixture of ore, cinders,
      etc., as the hearth of a puddling furnace.
   
   

2. \Fet"tle\, v. i.
   To make preparations; to put things in order; to do trifling
   business. [Prov. Eng.] --Bp. Hall.
   
   

3. \Fet"tle\, n.
   The act of fettling. [Prov. Eng.] --Wright.
   
   {In fine fettle}, in good spirits.