Roots

One root, a whole family of words — in both languages.

You already own the most powerful idea in Arabic. Hebrew taught you that three consonants carry a core meaning, and that patterns poured around them mint new words — the way כ-ת-ב gives you כָּתַב, מִכְתָּב, and כְּתוֹבֶת. Arabic runs on exactly the same engine, and very often on the very same roots. Learn one root here and you don't get one word — you get the whole family, plus the Hebrew relatives you grew up with.