quinquagesimussextus

lacesso, lacessere, lacessivi and -ii, lacessitum

Definition:

1. To challenge to a contest; to challenge (to provide an answer, proof, etc.); (poet.) to chance the hazards of, challenge (natural forces, etc);
2. To rouse to hostile, retaliatory, etc. action, provoke; to stimulate, rouse (the senses); to stir up, activate (inanim. things);
3. to provoke, arouse (an action or feeling, etc.);
4. to assail repeatedly, harass, worry, vex; (verbally); to disturb, trouble (the peace); to importune (w. two accs.) to importune (for)
5. To assail (with repeated blows); to disturb (physically), upset

Sententia: Balteus de corpore Pallantis lacessivit Aeneae iram tantam ut statim furatum id, Turnum, necaret.

The baldric from the body of Pallas aroused so great an anger of Aeneas that immediately he killed the one having stolen it, Turnus.

Nautae lacessere angustas aquas inter Siciliam et Italiam ob duplices minas Scyllae Charybdisque malunt.

Sailors do not prefer to challenge (or "chance the hazards of," though that is rather hard to remember) the narrow waters between Sicily and Italy on behalf of the twofold/double threats of Scylla and Charybdis.

The definition today again comes from the Oxford Latin Dictionary, having been consulted in a library and duly copied (and now cited!). This word is used quite a bit in Vergil, though not in any of the parts we read, and some in both Catullus and Ovid's Metamorphoses (though ditto about it not being in the parts in the syllabi).