To display a title in bold face is simple: just set title "{/:Bold <title>}"
When the title is not plain text, but a string variable... that does not work.
I've searched "face" and "set term" in the manual for getting some hint, but what they call 'face' therein, seems to be what is commonly called "font" (Arial, for example). Besides, does there exist one command so as to make all text bold (title, tics and labels)?