The word "mantra" is derived from two Sanskrit words. The first is "manas" or "mind," which provides the "man" syllable. The second syllable is drawn from the Sanskrit word "trai" meaning to "protect" or to "free from.
The word "tantra" is derived from the combination of two words "tattva" and "mantra". "Tattva" means the science of cosmic principles, while "mantra" refers to the science of mystic sound and vibrations.
Mantras are used for several purposes, for material gains and for spiritual upliftment. The most exalted aim can be spiritual upliftment, others include curing of disease, warding off evil, attaining liberation, gaining wealth, influencing others, acquiring powers, and at the lowest and meanest level, harming others.
Gayatri Mantra (the mother of the vedas), the foremost mantra in hinduism and hindu beliefs, inspires wisdom.
Chanting the Mantra of a particular planet for a specific number of times in a given time frame helps reducing the negative effects of the planet.