The root of دَعَا is د ع و. Alif appears in the perfect, while the final wāw survives in the indicative active imperfect. Active and passive derivations have distinct endings.
CategoryFormMeaning
Active perfectدَعَاhe called
Active imperfectيَدْعُوhe calls
Passive perfectدُعِيَhe was called
Passive imperfectيُدْعَىhe is called
Active participleدَاعٍcaller
Passive participleمَدْعُوٌّone called
Imperativeاُدْعُcall!
Prohibitionلا تَدْعُdo not call!
The short ḍammah at the end of the imperative and prohibition reflects the missing final wāw in the jussive structure.