In Bridge, should a defender "encourage" with a "stranded honor?
Yes I think hearts should be discouraged. Given West's lead is top of nothing then South must have the Ace and probably the ten too (if not its one of North's xs) so hearts are pretty disastrous, especially as West's lead has probably given declarer a free finesse.

Of course to really know we need to see the other suits in the visible hands (one would assume there either has to be a better suit to attack or defense has no chance)

It's also probably worth noting that top of nothing is usually a lead made when nothing better is available so we can probably infer that West has a poor hand to lead with.