Want- desire vs lack

When do you use want as "desire" and as "lack?" It appears quite often in texts, and I have a hard time differentiating the two.

For example:

The want of Miss Taylor would be felt every hour of every day.

The great family characteristic of the Stanhopes might probably be said to be heartlessness, but this want of feeling was, in most of them, accompanied by so great an amount of good nature as to make itself by little noticeable to the world.