" Ecthelion must be similarly from Aegthelion. Latter element is a derivative of √stel 'remain firm'. The form with prefix 'sundóma', estel, was used in Q{uenya} and S{indarin} for 'hope' – sc. a temper of mind, steady, fixed in purpose, and difficult to dissuade and unlikely to fall into despair or abandon its purpose. The unprefixed stel- gave [? S verb] thel 'intend, mean, purpose, resolve, will'. So Q ? þelma 'a fixed idea,..., will. "

― J.R.R. Tolkien , The War of the Jewels (The History of Middle-Earth, #11)