Source : Webster's Revised Unabridged Dictionary (1913)

Forsooth \For*sooth"\, n.
   A person who used forsooth much; a very ceremonious and
   deferential person. [R.]

         You sip so like a forsooth of the city.  --B. Jonson.

Forsooth \For*sooth"\, adv. [AS. fors[=o][eth]; for, prep. +
   s[=o][eth] sooth, truth. See {For}, prep., and {Sooth}.]
   In truth; in fact; certainly; very well; -- formerly used as
   an expression of deference or respect, especially to woman;
   now used ironically or contemptuously.

         A fit man, forsooth, to govern a realm!  --Hayward.

         Our old English word forsooth has been changed for the
         French madam.                            --Guardian.

Forsooth \For*sooth"\, v. t.
   To address respectfully with the term forsooth. [Obs.]

         The captain of the ``Charles'' had forsoothed her,
         though he knew her well enough and she him. --Pepys.

Source : WordNet®

forsooth
     adv : an archaic word originally meaning `in truth' but now
           usually used to express disbelief