Meaning and elaboration
Meaning: The One who is Perfectly Accomplished and Ever-Ready for Action.
Elaboration
The name Siddha means "perfectly accomplished," "fulfilled," "realized," or "one who has attained supernatural powers (siddhis)." As a name of Mahakali, it points to her as the very fullness of perfection and power.
Divine Perfection and Attainment Siddha expresses Kali's complete mastery over every aspect of existence. She is not moving toward perfection; she is perfection itself. Everything in her action, manifestation, and nature is already whole, exact, and effective. In the spiritual sense, she is the supreme guru, the one who embodies complete realization and enlightenment.
Source of Siddhis She is the source and bestower of all siddhis, whether they appear as lesser powers or as profound spiritual attainments. Devotees may worship her to receive such siddhis, not merely for display, but as aids in sadhana or in service of a higher good. Yet her greatest siddhi is not any extraordinary power. It is her power to lead the devotee beyond suffering and toward liberation.
Always Ready for Action The phrase "ever-ready for action" reveals her dynamic nature. Though she is perfectly accomplished, she is never inert. She remains ever-vigilant, ready to intervene, destroy negativity and evil both within and without, and protect her devotees. This readiness shows her active and unfailing grace, always poised to manifest her power for the welfare of the cosmos and the individual soul.
The Goal of Sadhana For the spiritual practitioner, to become siddha is the highest aim: to become perfected in sadhana, to realize one's true nature, and to attain liberation. By worshipping Kali as Siddha, devotees recognize her as both the ideal of spiritual fulfillment and the one who grants it.