The term WATCHFUL ONES can be broken down into four crossword solutions: EYES (4 letters), EYERS (5 letters), SPIERS (6 letters), and SENTINELS (9 letters). Eyes are organs of sight, and the act of looking or seeing is known as 'eyering'. Spiers are people who observe or watch closely, while SENTINELS are guards or watchers who keep a vigilant lookout. All of these terms refer to people who are alert and attentive, making them watchful ones.