Nonius Marcellus, Compendium of Doctrine, Vol. II

MONSTRA monsters/warnings and OSTENTA prodigies/signs are understood similarly, because they show and display imminent things. An OMEN prophetic sign/augury, however, is a vow of the mind and voice; whence it is said to those sacrificing: "Have good omens," that is, may those standing around desire with a right mind and utter good things from their mouths. A PORTENTUM portent is not only that which portends, but also that which draws out portents from those significations which are shown in auspices, auguries, and the inspection of entrails. A PRODIGIUM prodigy is always the worst thing, said as if it were a thing to be driven far away. Virgil, book III:

The new and unspeakable Harpy Celaeno
predicts a prodigium and announces sad angers.

INIURIA wrong/harm differs from CONTUMELIA insult/contumely in this. For iniuria is a lighter matter. Pacuvius in Periboea:

I suffer iniuria harm easily, if it is free from contumelia insult.

Caecilius in Fallacia:

I can bear misfortune easily, if iniuria harm is absent from it;
even iniuria, if contumelia insult is not set against it.

FULMEN lightning bolt/thunderbolt, FULGUR lightning flash, and FULGURITUM struck by lightning are separated by these understandings. For fulmen is the weapon itself which is thrown; as Virgil in Georgics, book I:

The father himself, in the midst of the night of clouds,
works with his flashing right hand to throw fulmina thunderbolts.