Today is the summer solstice, the day that starts the summer season, which also happens to be the day in which we have the most hours of sunlight. Merriam-Webster defines solstice as: one of the two points on the ecliptic at which its distance from the celestial equator is greatest and which is reached by the sun each year about June 22nd and December 22nd.
So, basically, what I said before. (Way to complicate things, M-W.)
English adopted solstice from the Old French word of the same spelling. The word originally came from Latin as a combination of sol, which means sun, and sistere, which means “to come to a stop.” Related is the Latin word solstitium, which means “point at which the sun seems to stand still.” (Much thanks to the Online Etymology Dictionary for that information.)