Merriam-Webster Collegiate Dictionary - constrain

 transitive verb  Etymology: Middle English, from Anglo-French ~dre, from Latin constringere to constrict, ~, from com- + stringere to draw tight — more at strain  Date: 14th century  1.  a. to force by imposed stricture, restriction, or limitation  b. to restrict the motion of (a mechanical body) to a particular mode  2. compress; also to clasp tightly  3. to secure by or as if by bonds ; confine; broadly limit  4. to force or produce in an unnatural or strained manner a ~ed smile  5. to hold back by or as if by force ~ing my mind not to wander from the task — Charles Dickens  Synonyms: see force  • ~edly adverb