|Easton's Bible Dictionary|
In our Lord's time the Jews had adopted the Greek and Roman division of the night into four watches, each consisting of three hours, the first beginning at six o'clock in the evening (Luke 12:38; Matthew 14:25; Mark 6:48). But the ancient division, known as the first and second cock-crowing, was still retained. The cock usually crows several times soon after midnight (this is the first crowing), and again at the dawn of day (and this is the second crowing). Mark mentions (14:30) the two cock-crowings. Matthew (26:34) alludes to that only which was emphatically the cock-crowing, viz, the second.
Noah Webster's Dictionary
(n.) The time at which cocks first crow; the early morning.
Int. Standard Bible Encyclopedia
kok'-kro-ing (alektorophonia): An indefinite hour of the night between midnight and morning (Mark 13:35), referred to by all the evangelists in their account of Peter's denial (Matthew 26:34, 74 Mark 14:30 Luke 22:34 John 13:38). It is derived from the habit of the cock to crow especially toward morning.
Cockcrowing (1 Occurrence)
Mark 13:35 Watch ye therefore: for ye know not when the master of the house cometh, at even, or at midnight, or at the cockcrowing, or in the morning: (KJV ASV)