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)
Origin: as. Forsoo; for, prep. _ soo sooth, truth. See For, prep, and Sooth.