WordWeb Online

1. Rigidly accurate; allowing no deviation from a standard
   "rigorous application of the law";
   - strict
    
2. Demanding strict attention to rules and procedures
   "rigorous discipline";
   - stringent, tight
    
3. Performed comprehensively and completely; not superficial or partial
   "a rigorous study";
   - exhaustive, thorough, thoroughgoing, in-depth
    
4. Without qualification; used informally as an (often pejorative) intensifier
   - arrant, complete, consummate, double-dyed, everlasting, gross, perfect, pure, sodding, stark, staring, thorough, thoroughgoing, utter, unadulterated
    
5. Painstakingly careful and accurate
   "our accountant is rigorous";
   - thorough

See also: careful, complete, demanding, exact, exacting, unmitigated

Encyclopedia: Rigorous