a. To stop trying to do something
b. A person who is the first to study and develop a particular area of knowledge, culture, etc that other people then continue to develop
c. To travel to or around an area or a country in order to learn about it
d. A person who is travelling in a car, bus train, plane or ship and who is not driving it or working on it
e.Something that is difficult to understand or to explain
f. A submarine (a ship that can travel underwater) that goes underwater for short periods
g. To send an electronic signal, radio or television, broadcast , etc.
h. A long journey, especially by sea or in space