plainful adjective 2noun 1forms 3 adjective2 •Plain; obvious.So plainful clear to me, it followed as the night the day. — 2012 •(no longer used) Full of lamentation.Mark, O, ye beauties l—gay, and young, Mark the plainful woes, and weeping, That, from forc'd concealment sprung, Punish the sin of secret keeping. — 1780 noun1 •As much as a plain contains.Did some mythical giantess in the creation of this earth playfully prepare her desserts by the plainfuls? — 1984 formsplainfuls · more plainful · most plainful