That is, a meal taken after waking up. Something of a $20 word, to be used when being self-consciously elevated in tone. Compare prandial, relating to a meal, especially dinner. Just as different cultures at different times make the largest meal of the day either at mid-day or in the evening, so do they put less or more emphasis on the early morning meal. From Latin jentaculum, a breakfast taken immediately on getting up.
Just as completed my pre-jenticular exercises, it began to rain.