Learn Icelandic: Það er erfitt að græða peninga.

Yes, græða has multiple meanings. When used with peningar (money), it means "to profit" or "to make money". It is the standard verb for generating wealth or earning a return, whereas using a direct translation like gera (to make) would sound like you are physically manufacturing bills and coins.

Why is peninga in the plural form? Isn't money a singular concept?

In Icelandic, the noun peningur literally means "a coin" when singular. To talk about "money" in a general, uncountable sense, you must use the plural form peningar. Here, it takes the accusative plural form peninga because it is the direct object of the verb græða.

If peningar is a masculine noun, why is the adjective erfitt in the neuter form?

The adjective erfitt (hard/difficult) is agreeing with the dummy subject það (it), which is a neuter pronoun. It does not agree with peninga, which belongs to the infinitive phrase later in the sentence.

Could I use þéna instead of græða in this sentence?

Yes, you could say að þéna peninga. The difference is subtle: þéna implies earning money through steady work (like a salary), while græða leans more toward making a profit, generating wealth, or making money in a broader or more entrepreneurial sense.