Though you have a different goal, this is almost a duplicate of this question. However, much of the information in the answers there is hopelessly outdated by now, so I'll leave it to others to decide whether your question should stand on its own.
The advice to "run dungeons" is still the best I can give. It's what I did in my limited time to get the last few hundred gold for my legendary Twilight. What's changed since the other question was asked and answered is that the reward structure for dungeon runs mean that, to maximise your gold, it's really only worth doing each dungeon path once a day.
So my recommendation would be to do the following:
1) Level a character up to 80 if you haven't already, ideally a warrior (due to the perception that their DPS is the best in the game), although groups seem to have become more tolerant of diversity, and equip your character with decent gear (at least exotics if you don't have ascended yet) and use a decent build.
2) Learn at least the following dungeon explorable paths (complete story mode first so you can open them):
- CoF - path 1 & 2
- TA - Up & Forward path
- AC - all paths
3) Run each of these paths once per day (same reset time as the dailies).
If you've been playing the game for a while, I'd assume you've got step 1) done a long time ago, and most of step 2) as well. If you still need to learn dungeons, find a guild that does them regularly and uses TeamSpeak/Mumble/etc. to communicate. Or watch some youtube videos of quick dungeon runs and learn from them. You need to know where to stand for certain fights (e.g. stacking on a corner can sometimes prevent the group from taking damage while allowing you to DPS a boss), which mobs you can skip, when to change utilities to have stun breakers and stability when running past TA mobs, etc.
Step 3) gets you one gold per path (1g50s for AC), plus 26 silver, plus gold from kills, plus dungeon tokens, plus some drops to sell or salvage, plus materials and magic find from salvaging. Including the time it takes you to find a group for each run (use the in-game LFG tool, learn which groups are too elitist for you to join and start your own if there isn't one available), it should be possible to do between 5 and all 7 of these paths in two hours (of course you can do others, like Caudecus etc., the ones above are just the ones I've found to be easiest/quickest/most groups available). Less while you're still learning, more when you've got it down and have a good group to do them with. All of these should take between 10 minutes (less for CoF P1 with a good DPS group) and 20 minutes, sometimes a bit more if one or two group members don't know the paths well. Knowing how to manage your inventory so you don't have to run to a merchant between each dungeon should be a given, i.e. have a few salvage kits, know what to sell on the TP and what to salvage, and have enough space for stuff you want to keep.
So assuming you only get to do 5 of these a day, that should still net you at least 8 gold, give or take. When you become better, 2 hours should get you 10-12 gold. I don't know of any other method that gets you anywhere near as much gold, unless you're an expert TP flipper (but to do that, you need a LOT of capital to start with).