Source : Webster's Revised Unabridged Dictionary (1913)

Gruff \Gruff\, a. [Compar. {Gruffer}; superl. {Gruffest}.] [D.
   grof; akin to G. grob, OHG. gerob, grob, Dan. grov, Sw. grof,
   perh. akin to AS. rc['o]fan to break, Z. reavc, rupture, g-
   standing for the AS. prefix ge-, Goth. ga-.]
   Of a rough or stern manner, voice, or countenance; sour;
   surly; severe; harsh. --Addison.

         Gruff, disagreeable, sarcastic remarks.  --Thackeray.
   -- {Gruff"ly}, adv. -- {Gruff"ness}, n.

Source : WordNet®

gruffly
     adv : in a gruff manner; "`No,' he replied gruffly"