1.  to loosen;  to slacken
2.  to relax (attention, efforts, etc.);  to let down (one's guard);  to relieve (tension)
3.  to relax (a rule);  to ease (e.g. restrictions);  to loosen (control)
4.  to reduce (speed);  to slow down;  to ease up
5.  to make more gradual (of a slope)