Cases of word usage

1) a person who goes, or is often or always with, another (companion)

2) the state of always being the same in standard, form, behaviour etc (consistency)

3) the theory that our actions are always caused by the desire to benefit ourselves (egoism)

4) firmly attached or fastened; always the same (fixed)

5) (of lines) always at the same distance from one another; similar (parallel)