Xresources
From Attie's Wiki
Below is the entire contents of my '~/.Xresources' file:
! Xterm stuff XTerm*background: black XTerm*foreground: white XTerm*cursorColor: white XTerm*scrollBar: false XTerm*vt100.geometry: 120x40
Or for a 1920x1080 'ready' terminal, use
XTerm*vt100.geometry: 280x70