Forts are very similar to castles but they were exclusively used for the military purposes. A fortress is a very large fort.

The two differ in their spelling, but do not have different meaning. Axis is the singular form, whereas axes are the plural form of an axis.

Motivation is related to inspiration that increases the eagerness or willingness to do work. Encouragement is the persuasion to do or to continue something.

The two words differ in their spelling, and actually have different meanings too. A lier is the one who lies down; while a liar is the one who deliberately tells lies.

Inspiration is the process by which the mental stimulation takes place. It makes one want to do or feel something. Motivation is related to inspiration that increases the eagerness or willingness to do work.