Physics:

Scientific Definition: The study of matter, energy, and the fundamental forces that govern their interactions.

Etymology: From Greek "physis" (nature) and "ikos" (related to), meaning related to nature.

Chemistry:

Scientific Definition: The study of the properties, composition, and behavior of matter.

Etymology: From Arabic "al-kīmiyā" and Greek "khemeia" (transmutation), referring to the ancient practice of transmuting base metals into gold.

Biology:

Scientific Definition: The study of living organisms and their interactions with each other and their environment.

Etymology: From Greek "bios" (life) and "logia" (study), meaning the study of life.

Geology:

Scientific Definition: The study of the Earth's physical structure, composition, and history.

Etymology: From Greek "ge" (earth) and "logia" (study), meaning the study of the Earth.

Astronomy:

Scientific Definition: The study of celestial objects, space, and the universe as a whole.

Etymology: From Greek "astron" (star) and "nomos" (law), meaning the laws of the stars.

Astrophysics:

Scientific Definition: The branch of astronomy that deals with the physical properties and interactions of celestial objects and phenomena.

Etymology: "Astro" from Greek "astron" (star) + "physics" from Latin "physica" (natural things), 

meaning natural things related to stars.

Cosmology:

Scientific Definition: The study of the origin, evolution, and large-scale structure of the universe.

Etymology: From Greek "kosmos" (world, universe) and "logia" (study), meaning the study of the universe.

Quantum Mechanics:

Scientific Definition: The branch of physics that deals with the behavior of very small particles and the interactions of matter and energy at the quantum level.

Etymology: "Quantum" from Latin "quantus" (how much) + "mechanics" from Greek "mekhanē" (machine), meaning how much machine-like behavior.

Relativity:

Scientific Definition: Einstein's theory that describes the relationships between space, time, and gravity, including special and general relativity.

Etymology: From Latin "relativus" (having relation or reference) and "relatus" (carried back), indicating a sense of comparison.

Astrolabe:

Scientific Definition: An ancient instrument used to measure the position of celestial objects and determine latitude.

Etymology: From Greek "astron" (star) and "lambanein" (to take), meaning to take the stars.

Celestial Sphere:

Scientific Definition: An imaginary sphere with Earth at its center, used to model the apparent positions of celestial objects.

Etymology: "Celestial" from Latin "caelum" (sky) + "sphere" from Greek "sphaira" (ball), meaning sky ball.

Equinox:

Scientific Definition: The two points in the year when the day and night are approximately equal in length.

Etymology: From Latin "aequus" (equal) + "nox" (night), meaning equal night.

Solstice:

Scientific Definition: The two points in the year when the sun reaches its highest or lowest point in the sky at noon, marking the longest and shortest days.

Etymology: From Latin "solstitium" (sun-stopping), referring to the sun appearing to stop and change direction during these points.

Eclipse:

Scientific Definition: The obscuring of one celestial body by another, such as a solar or lunar eclipse.

Etymology: From Greek "ekleipsis" (abandonment) and "ekleipein" (to leave out), referring to the temporary disappearance of a celestial body.

Gravity:

Scientific Definition: The force of attraction between objects with mass, responsible for the motion of planets and other celestial bodies.

Etymology: From Latin "gravitas" (weight) and "gravis" (heavy), referring to the weightiness of objects.

Planet:

Scientific Definition: A celestial body that orbits a star, is spherical in shape, and has cleared its orbit of other debris.

Etymology: From Greek "planētēs" (wanderer), as planets were observed to move against the fixed backdrop of stars.