1. (研究、解释)理论的，理论性的
A theoretical study or explanation is based on or uses the ideas and abstract principles that relate to a particular subject, rather than the practical aspects or uses of it.
e.g. ...theoretical physics.
理论物理学
2. 理论上的;推想的
If you describe a situation as a theoretical one, you mean that although it is supposed to be true or to exist in the way stated, it may not in fact be true or exist in that way.
e.g. This is certainly a theoretical risk but in practice there is seldom a problem...
从理论上讲，这肯定是有风险的，可是实际上很少出问题。
e.g. These fears are purely theoretical.
这些担忧纯粹是臆测出来的。