Today is Guru Purnima, a festival celebrated by the Hindus, Buddhists, and Jains in honour of the guru-s. Among Hindus, the festival is also called Vyasa Purnima, for it is believed that Veda Vyasa was born on this day. The Sikhs also have a festival Guru Parb, but that is celebrated on a different day.
As per the Concise Oxford English dictionary, the English word guru has three meanings: (1) a Hindu spiritual teacher, (2) each of the ten first leaders of the Sikh religion, and (3) an influential teacher or expert, for example "a management guru".
As one can guess from the first and second meanings, the word guru in English comes from Hindi and Punjabi. In turn, the word guru and Hindi and Punjabi comes from the Sanskrit word guru.
The Online Etymology Dictionary traces the Sanskrit guru to Proto-Indo European (PIE) *gwere in the sense of "heavy". The Latin word gravis meaning "heavy" is also believed to derive from PIE *gwere. English words related to gravis are grave (meaning weighty, as in "a grave matter"), gravitate, gravimeter, and gravity.
Interestingly, the word for the scientific concept of gravity is gurutvakarshana in many Indian languages including Hindi, Marathi, Telugu, and Gujarati. The first part of this word is gurutva, which means the quality of being guru or heavy.
"Heavy" is one of the primary meanings of guru in Sanskrit also. However, the word is customarily used in many other meanings in Sanskrit. Here is a list of thirty-four meanings of the word guru based on the citations in the nineteenth century lexicons Shabda-kalpa-druma and Vachaspatya.
(1) "one who swallows ignorance". Indian etymologists in the first millennium BCE derived guru from the root gri ("to swallow"). The same root gives the Sanskrit word nigarana ("swallowing"), from which comes the Hindi word nigalna ("to swallow").
(2) "one who teaches dharma and scriptures". The root gri also means "to speak" or "to instruct" in Sanskrit. The meaning is from this sense of the root.
(3) "one who is praised by gods, gandharva‑s, humans, etc". This comes from the passive sense of gri ("to speak").
(4) "one who destroys darkness (=gu) with brilliance (=ru)". This meaning is as per the Guru Gita, which is a part of the Skanda Purana. In the latter half of twentieth century, the Guru Gita was popularized in the West by Swami Muktananda of the Siddha Yoga movement.
(5) "one by whom darkness (=gu) is destroyed (=ru)". This meaning is also from the Guru Gita.
(6) "one by whom the disease of worldly existence (=gu) is removed (=ru)". This meaning is also from the Guru Gita.
(7) "one who is beyond qualities (=gu, standing for gunatita) and beyond form (=ru, standing for rupatita). This meaning is also from the Guru Gita.
(8) "one by whom the bondage of maya (=gu) is released (=ru)". This meaning is also from the Guru Gita.
(9) "Brahma (the creator)". Brahma is called guru in the Kashi-khanda of the Skanda Purana.
(10) "Vishnu". Vishnu is called both guru and gurutama ("the most superior guru") in the Vishnu Sahasranama of the Mahabharata.
(11) "Shiva". Shiva is called guru in the Shiva Sahasranama, also in the Mahabharata.
(12) "The Supreme Brahman". Towards the end of George Harrison's single My Sweet Lord(1971), which was top of the charts globally, the chorus sang the famous Guru Gita verse listing the meanings (9) to (12): gurur-brahma gurur-vishnuh gurur-devo maheshvarah, guruh sakshat para-brahma tasmai shri-gurave namah.
(13) "Brihaspati, the teacher of the gods". This is why Thursday, named after Jupiter, is called both guru-vaar and brihaspati-vaar in Hindi.
(14) "Prabhakara, the teacher of Mimamsa philosophy". Mimamsa is one of the six orthodox schools of philosophy in Hinduism.
(15) "Dronacharya, the teacher of the Pandava‑s and Kaurava‑s". Dronacharya, after whom the Dronacharya Award is named, is often called Guru Dronacharya or simply Guru Drona.
(16) "one who performs nisheka rituals". The nisheka rituals are Hindu ceremonies like garbhadhana, etc.)"
(17) "one who gives a mantra". This is why many mantra-s are referred to as guru-mantra.
(18) "the father". The feminine form of guru is gurvi, one of whose meaning is "the mother".
(19) "any of the eleven male elders". The eleven male elders consist of the teacher, the father, elder brothers, maternal uncles, paternal uncles, maternal grandfathers, paternal grandfathers, father-in-law, protectors, king, and community elders.
(20) "any elder in general". This group is called guru-varga and includes not only teachers, parents, elder siblings, uncles/aunts, parents-in-law, and grandparents, but also any protectors, the midwife, and the king.
(21) "one who is great".
(22) "one who is ageless".
(23) "one who is large".
(24) "one who is powerful"
(25) "one who is honourable". The abstract noun derived from guru is garima which has meanings corresponding to (21) to (25), i.e. greatness, largeness, honour/dignity, etc.
(26) "one whose speech has profound meaning".
(27) "heavy". It is this sense of guru from which modern words gurutva or gurutvakarshanameaning gravity are derived.
(28) "one who grants siddhi-s (=gu), burns sins (=r), and is same as Shiva (=u)". This meaning is as per Agamasara, a Tantra work.
(29) "one who for the sake of attainment of jnana (=gu) illuminates the truth (=r) and bestows oneness with Shiva (=r)". This meaning is also as per Agamasara.
(30) "abundance". The first verse of Kalidasa's Meghaduta ("the cloud messenger") uses the word guru in this sense.
(31) "a long syllable". This is the meaning of guru in the context of Indian prosody, a field where the concepts and/or examples of Fibonacci sequence, Pascal's triangle, and de Bruijn's sequence were known much before Leonardo Fibonacci, Blaise Pascal, and Nicolaas Govert de Bruijn lived.
(32) "the Pushya constellation". Pushya is one of the 27 constellations in Indian astronomy.
(33) "the velvet bean creeper (Mucuna pruritus)".
(34) "the foxtail millet grass (Panicum italicum)". Coincidentally, millets are called mote anaj ("fat grains") in Hindi, and Sanskrit guru also means large (23) and heavy (27).
Thus, the word guru, which means "heavy", is indeed heavy for it is pregnant with so many meanings in Sanskrit. When one considers this fact, the word can be considered an autological word, defined by Wikipedia as "a word that expresses a property that it also possesses."
With that, I wish you a very Happy Guru Purnima 2017.