The internet isn't being to reliable in giving me a good understanding of the word Opum.
I believe it is the plural of Opus, meaning work(s) (as in, created works, like a sculpture or composition). Google says it is the plural of Ops, so Opum in this sense means wealth and food.
What do you think?
There are actually two different words involved here:
1) opus, genitive singular operis, genitive plural operum (neuter gender), which, as you correctly say, often refers to a created work.
2) ops, genitive singular opis, genitive plural opum (feminine gender), which, in the singular refers to might or power, but in the plural (opes, genitive opum) refers to wealth or resources, often military resources, as in Caesar's Commentarii.
Note that the two words have different genitive singulars (operis vs. opis) and different genitive plurals (operum vs. opum).