Theophylact Simocatta, Histories 2.4.1, comments on the word: "the Persian baggage, which it is customary for the Romans to call touldon in the local language." (This statement does not guarantee that the "local language" was Latin: see below.) Eventually it becomes the standard word for the baggage train in the Byzantine army. It most often appears as neuter (hence the current headword could be nominative or accusative), but it is also sometimes treated as masculine, tou=ldos, in e.g. ps.-Marcianus, Strategicon 1.3.24). In Latin sources it appears as neuter tuldum.
The word occurs frequently in Byzantine historians and military writers; cf. alpha 3526, sigma 24. Sophia Gyftopoulou discusses the etymology (pp. 84-86): perhaps related to Latin tuli, perfect of fero, perhaps Germanic, or perhaps from Avar or Turkish language.