The Morgengabe, according to Cancianus (Leges Barbarorum, tom. iv. p. 24.), was at first a free gift made by the husband after the first marriage night. This was carried to such excess, that Liutprand ordained
"Tamen ipsum Morgengabe volumus, ut non sit amplius nisi quarta pars ejus substantia, qui ipsum Morgengabe dedit."
This became subsequently converted into a right termed justitia.
Upon this extract from a charter,—
"Manifesta causa est mihi, quoniam die ilio quando te sposavi, promiseram tibi dare justitiam tuam secundum legem meam [qr. my Lombard law in opposition to the Roman, which he had a right to choose,] in Morgencap, id est, quartam portionem omnium rerum mobilium et immobilium," &c.
Cancianus thus comments:—
"Animadverte, quam recte charta hæc cum supra alligatis formulis conveniat. Sponsus promiserat Morgencap, quando feminam desponsaverat, inde vero ante conjugium chartam conscribit: et quod et Liutprandi lege, et ex antiquis moribus Donum fuit mere gratuitum, hic appellatur Justitia secundum legem Langobardorum."
The Morgencap here assumes, I apprehend, somewhat the form of dower. That it was so, is very doubtful. (Grimm, vol. ii. p. 441. "Morgengabe.")
"An demselben Morgen empfängt die JungFrau von ihrem Gemahl ein ansehnliches Geschenk, welches Morgengabe heisst. Schon in der Pactio Guntherammi et Childeberti, werden Dos und Morganagiba unterschieden, ebenso Leg. Rip. 37. 2. Alaman. 56. 1, 2. Dos und Morgangeba; Lex Burgend. 42. 2. Morgangeba und das 'pretium nuptiale;' bei den Langobarden, 'Meta und Morgengab.'"
I do not say this answers the question of your correspondent G., which is, what is the derivation of the word?