1. thelo means to wish or desire, and is the emotional element which leads to the consequent action.  It is therefore stronger than boulomai, because the natural impulse is stronger than the reasoned resolve.
   
   
2. The Noun thelema must also be noted, with the same distinction from boulema, as denoting the desire rather than the resolve.
   
   
3. boulomai, though it sometimes means more, yet has reference to the result of thelo; viz. the deliberate determination, whether in accordance with, or contrary to, the original wish or impulse.
   
   
4. In like manner the Noun boulema is to be distinguished from thelema (No. 2) as denoting resolve, counsel, or determination, rather than the wish or desire.  Boulema occurs only twice, Acts 27:43.  Rom. 9:19.  The Noun, boule with a similar meaning, occurs twelve times.

For illustrations of the differences see Matt. 1:19.  Mark 15:9, 12, 15.  Rom. 7:15, &c.