How are the words season, equinox and solstice related ? ?

They are all related to what time of year it is.

The solstices and equinoxes are all phenomenon that occur during certain seasons. There is a summer solstice and a winter solstice. The winter solstice is the shortest day of the year, as the summer solstice is the longest day of the year. During the solstice the sun is either at the highest point or the lowest point at noon. The Equinox is when the sun crosses the celestial equator, making day and night equal length. Equinox happens twice a year, during fall and spring.