Sidereal and synodic are correlated to the period of bodies in orbit. Sidereal can be described as the time required for one period to repeat in reverence to the stars. On the other hand, synodic can be described as the time necessary for one period to repeat with respect to a solar body. The synodic period is also referred to as the position of objects in relation to the sun. A cycle from one full moon to another full moon describes the synodic cycle.
On the contrary, a sidereal period demonstrates the rotation of the earth once a day with respect to the stars. A sidereal period also refers to the position of the object in relation to the stars. After a sidereal month, the moon is pushed back a little more to position itself with the earth. A thoughtful way to distinguish between the two is remembering that sidereal means star, while synodic means to join or come together.
Sidereal is a term that talks about the measurement of time relative to the position of the stars. In other words, it can be defined as the time it will take one period to repeat relative to the position of the stars. Also, sidereal can be defined as the position of objects relative to the stars. Synodic, on the other hand, refers to the measurement of time relative to the position of a solar body. You can also define synodic as the position of objects relative to the sun. A perfect example of a synodic cycle is the period between a full moon and another full moon. The sidereal month is not as long as the synodic month. It takes 29 days, 12 hrs, and 44 mins for a synodic month. On the contrary, it takes 27 days, 7 hrs, and 43 mins for a sidereal month. When you compare a sidereal year and a synodic year, you will see that the former is 20 mins shorter than the latter.
When you say a sidereal month, you are referring to the time when the moon will take one full revolution around the earth. This will happen with respect to the background stars. The sidereal month is going to be shorter as compared to the synodic month. The sidereal month will only last for a little more than 27 days (27.322) while a synodic month will last for more than 29 days (29.531). When someone says that something will take as long as a sidereal, this means that this is the required time for one period to happen that is in relation to the stars. Synodic, on the other hand, will take into consideration the position of the various objects but it will depend on the sun.