The creature Gothmog at the Siege of Minas Tirith

[Gordis]

Originally Posted by Inziladun

It appears to me 'Angmar' simply refers to the region.

Not in this quote, speaking of events of TA 3018 following the disaster at the ford of Bruinen. Here is the fuller quote:

Only the bodies of 8 horses were discovered; but also the raiment of the Captain. It is probable that the Captain took the one horse that remained (he may have had strength to withdraw it from the flood) and unclad, naked, invisible, rode as swift as he could back to Mordor. At swiftest he could not accomplish that (for his horse at least would need some food and rest, though he needed none) ere November had passed. The wrath and fear of Sauron then may be guessed; yet if there was any in the world in whom he trusted it was the Lord of Angmar; and if his wrath were lessened by perceiving that his great servant had defeated by ill chance (and the craft of the Wise) rather than by faults of his own, his fear would be the more – seeing what power was yet in his Enemies, and how sharply fortune favoured them at each turn when all seemed lost. Help no doubt was sent out to the other Ringwraiths as they made their way back, and they were bidden to remain secret again. It was no doubt at the end of 1418 that Sauron (S. likely aided by Angmar) bethought him of the winged mounts; and yet withheld them, until things became almost desperate and he was forced to launch his war in haste. RC p.262-3