jentacular
Of or pertaining to breakfast; specifically, one taken early in the morning or immediately upon getting up.
archaic
I took a post-jentacular walk to settle my stomach.
Where it comes from
Learned borrowing from Latin iēntāculum (“breakfast (particularly taken right after getting up)”) + English -ar (suffix meaning ‘of, near, or pertaining to’ forming adjectives). Iēntāculum is derived from ientō (a variant of ieientō (“to have breakfast”), ultimately from Proto-Indo-European *h₁yaǵ- (“to sacrifice; to worship”)) + -culum (diminutive suffix).
Adapted from the Wiktionary entry jentacular (CC BY-SA 4.0).