text(x, y, font=2, \"text\")
changes the font of the whole \'text\'.
But is it possible to change the font of a single word in \'text\'?
Yep!
plot.new() text(0.5,0.5, expression(paste(bold("bold")," not bold")))
Take a look at ?plotmath for a whole slew of other options and symbols that can be used.
?plotmath