Nictitate is an intransitive verb meaning to blink or wink. The word originates from the Latin word nictitare, meaning to blink. Nictitate entered the English lexicon in the early 1800s.
For most organisms with eyeballs, blinking is an essential task. Blinking helps to cleanse and moisten the eyes. While us humans only have an upper and lower eyelid, owls have a third eyelid called a nictitating membrane which is used to provide moisture to the eyes and to protect them from damage from foreign objects during flight.
Owls are particularly cute at this basic function and each eye can blink independently of the other. Case in point: this adorable female Red Morph Eastern Screech Owlet peeking out from her tree hollow. Watching her calmly observe is mesmerizing as she slowly nictitates one large yellow eye at a time, sometimes both at the same time.