unsleeping
Word family
Synonym discussion
Sense: adjective/1
These words all touch on staying alert, but they differ in tone and focus. 'Vigilant' is the everyday choice: it stresses careful, ready watching for danger, as a security guard or a worried parent might be. 'Wakeful' is plain and physical — it simply means not asleep, and says nothing about duty or effort. 'Tireless' shifts the focus to endless work rather than staying awake, so a tireless campaigner keeps going without rest. 'Unsleeping' is the most literary and dramatic of the group, picturing something that never once stops guarding or caring — an unsleeping watch, an unsleeping eye. Compare: a guard stays vigilant on duty, a child is wakeful past midnight, a nurse is tireless during a long shift, but only a poem speaks of the city's unsleeping lights.
Common collocations
Etymology
Formed in English by adding the negative prefix 'un-' (meaning 'not') to 'sleeping', the present participle of the old verb 'sleep'. 'Sleep' goes back to Old English 'slǣpan', shared with German 'schlafen'. The 'un-' prefix has marked the absence of a quality since Old English, so 'unsleeping' literally pictures something that does not sleep, and from there came to suggest tireless watching or effort.