Before Newton many phycisists try to understand nature and the rotations of planets. But Newton founded his laws of gravity. But was he the first who used the word gravity or when was it first used? And comes the word gravity from the word 'grievous'? Or was Aristotle or Galilei before him using that word? Of course they spoke another language but perhaps the already used βαρύτητα or gravità?
Let us then apply the term ‘heavy’ (βάρος) to that which naturally moves towards the centre, and ‘light’ to that which moves naturally away from the centre. (De Caelo, 269b)
Isaac Newton uses gravity in his Philosophiae Naturalis Principia Mathematica (1687, 3rd Latin ed, 1726):
A centripetal force is that by which bodies are drawn or impelled, or any way tend, towards a point as to a centre.
Of this sort is gravity [gravitas], by which bodies tend to the centre of the earth.
Thus, Newton did not invent the word, but was the author of a crucial "shift of meaning": previously "gravity" denoted a quality, then a force.
For sure, Newton "invented" the force of gravity [vi gravitatis].
Note. Galileo Galilei in his Dialogue (in Italian) uses: gravità and leggerezza for heaviness and lightness, respectively.
This is a supplement to the two (good) answers by @Mauro Allegranza and @Viktor Blasjo. Although these answers and the question now have some age to them, it seems worth clarifying them by adding some historical perspective to the questioner's (largely mistaken) opening statement that "Before Newton many phycisists try to understand nature and the rotations of planets."
Before Kepler, astronomy was not thought to be a matter of physics, certainly not in the modern universal sense. For a long time, the idea held sway that the world consisted of two parts, quite different from each other (see Lindberg & Shanks (eds.)(2013) 'Cambridge History of Science', vol.2). The lower part was a "terrestrial region extend[ing] downward from the concave surface of the lunar orb to the center of the Earth", a "realm of incessant change", made from the four primary qualities "hot, cold, dry, and moist" or the elements representing them, fire, earth, air, water. In radical contrast, the upper part, the heavens above the sphere of the moon had attributes of perfection and incorruptibility. The heavens were not made of the four terrestrial elements, they were composed of a fifth and aetherial element, or "quintessence", and their motions showed the perfections of pure geometry in uniform circular motions. Within this framework of incorruptible celestial quintessence and perfect geometry it made no sense to think of physics learned from terrestrial effects as having any role.
The title of Kepler's book of 1609 is sometimes abbreviated just to 'Astronomia nova' or 'New astronomy'. More fully, his title in translation runs "A new astronomy, studied by causes, or, Celestial Physics". Kepler's idea that the celestial motions were subject to physical causes was itself revolutionary. He ran into conservative objections, made stiffer by the fact that he not only departed (especially with his postulated elliptical orbits) from the geometrical perfections of circular motion; he also demanded calculations that could not be perfectly executed by traditional demonstrative methods of geometry: they could only be approximated ('Kepler's problem' in Kepler (1609) chap.60, forerunner of the later 'Kepler's equation').
Kepler's ideas were rather slow to find limited acceptance. His elliptical orbits gained credibility by the success of his Rudolphine Tables (1627), especially in predicting a 1630 transit of Mercury across the sun's disk (see e.g. Gingerich (2013)). But the particular physics that he proposed, to implement his overarching idea of physical causes in astronomy, was not a success: it involved a power of the sun, by virtue of its rotation (and by the help of something like outwardly extending magnetic fibers) to drive the planets around their orbits. The special inequalities of the moon's motion, Kepler supposed, were effects of the sun's illumination. Kepler also thought that if not for the sun's rotatory drive, the orbital motions would cease and come to rest. (See Bruce Stephenson (1985) 'Kepler's Physical Astronomy'.) The particular physics that Kepler conceived was rather speedily forgotten, even though his overarching general idea of the existence and relevance of celestial physical causes did succeed much later in the hands of others.
There are other indications that a number of respected geometrical astronomers of even the mid-17th century did not regard astronomy as governed by physics, quite apart from the question of Kepler's elliptical ideas.
Thus G B Riccioli's 'Almagestum Novum' (1651) disparaged the efforts of those such as Cavalieri who had tried to give quantitative account of the core of Kepler's elliptical astronomy, calling these efforts an unsuccessful attempt to "apply medicine" to the "a-geometrical" relationships of Kepler's orbital ellipses -- as if Kepler's 'departure' from geometry was a kind of sickness in itself.
Even 60 years after the publication of Kepler's 'Astronomia nova...', Nicolas Mercator (1669-70) could still report complaints about Kepler's hypotheses (Philosophical Transactions 1670, vol.5, pp.1168-1175). At p.1174 (translated from the Latin):
"No-one has been found up to now who would deny that Kepler's areas can satisfy the appearances; but since neither he himself nor anyone after him could determine them by direct calculation, some have criticized Kepler for having parted ways with geometry while indulging too much in [speculation about] physical causes."
Mercator's remarks bear witness to contemporary opinions that still regarded it as a mistake on Kepler's part even to propose introducing physics into astronomy. The conservatives included I Boulliau, who accepted ellipses, but sought to relace Kepler's ideas about the associated celestial motions by something purely geometrical, and GB Riccioli whose scepticism was already cited above.
To be sure, the older ideas were breaking down during the 1670s. A number of thinkers (including those acknowledged in Newton's 'Principia' book 1 prop.4 and elsewhere, Wren, Hook, Halley) were starting to apply physical ideas to orbital motions, and Hooke in particular made the insightful inference from his observation of apparent impact craters on the moon that the moon, too, had an attractive power to make heavy objects fall towards it. But nearly all physics was terrestrial, and Newton's proposal, quoted by @Viktor Blasjo, that the force retaining the moon in its orbit was of the same kind as the familiar heaviness seen in terrestrial objects, was revolutionary in itself.
So this background tends to explain and support Mauro Allegranza's answer that Newton did not invent the word gravity, but he was the author of a crucial "shift of meaning" in it.