Evolution of the word Graha ग्रह

The word graha more literally means “grasp.” Various forms of the word graha are used in Sanskrit very similarly with how we use the word “grasp” in English. For example:

अथः श्रीकृष्णनामादि नभवेत्ग्रह्यम् इन्द्रियै (athaḥ śrī kṛṣṇa-nāmādi na bhaved grahyam indriyai) {“Description of Krishna by names and words is not within the grasp of the senses.”}

As is common in any language, things with certain qualities are often referred to by naming that quality. So a class of monster gained the name Graha – evil spirits who possessed human beings. Because these spirits took hold of (“grasped”) the human being, they were named “the seizers” – Graha. Even our word for an epileptic episode comes from the idea that Graha (“Seizers”)  cause such things (“Seizures”).

Rahu was originally a demonic being, much more powerful than a Graha. But when he became a “semi-planet” he caused Eclipses. In an eclipse Rahu “seizes” the sun and moon, therefore, Rahu, specifically began to be called a “Graha.”

As time wore on the word Graha became applied to all the planets.

Thus today the term graha can even be used to indicate the number nine! (Since there are nine planets)

– Vic DiCara (www.vicdicara.com)

Rahu and Ketu- the waxing and waning moon