The <blink> tag was removed from the HTML standard years ago because it was so horribly over-used that it annoyed everyone, and they were afraid it might trigger epileptic fits.
No browser or recent HTML software library supports that tag.
Animated GIF images don't work inline with the text either, so at the moment you can only have flashing text in the graphics window. (and you would need software that makes animated GIFs)

- HTMLBlinkElement.gif (1.09 KiB) Viewed 175 times
You could do something with timed events though, clearing and re-writing the screen.
With two sub events of 1 second duration, one could write the screen of text with the flashing word included and the other with it replaced with spaces.
This would look like that word is flashing at half a hertz.
You would have to stop the event when the player enters any command, perhaps using a priority 1 "*" task with the "Continue executing matching lower priority tasks" option?