In an earlier sentence this meant profusely, but that was marked wrong here,
That's how I just tried to translate it, too. Does it have to be yn helaeth to mean profusely?
Yes. On its own, helaeth is an adjective.
Helaeth also means Ample and when used as a verb Helaethu meaning Amplify. I feel some of these translations do not completely cover what should be accepted as correct.
It's often possible to find a number of potential translations for one word, but since each response needs to individually input into the system, it's only practical to include a few.
No matter how many translations that are written correctly for a word, I feel that they all should be accepted. It causes confusion for a learner of any language.