Source : Webster's Revised Unabridged Dictionary (1913)

Rigid \Rig"id\, a. [L. rigidus, fr. rigere to be stiff or numb:
   cf. F. rigide. Cf. {Rigor}. ]
   1. Firm; stiff; unyielding; not pliant; not flexible.

            Upright beams innumerable Of rigid spears. --Milton.

   2. Hence, not lax or indulgent; severe; inflexible; strict;
      as, a rigid father or master; rigid discipline; rigid
      criticism; a rigid sentence.

            The more rigid order of principles in religion and
            government.                           --Hawthorne.

   Syn: Stiff; unpliant; inflexible; unyielding; strict; exact;
        severe; austere; stern; rigorous; unmitigated.

Source : WordNet®

rigid
     adj 1: incapable of or resistant to bending; "a rigid strip of
            metal"; "a table made of rigid plastic"; "a palace
            guardsman stiff as a poker" [syn: {stiff}]
     2: incapable of compromise or flexibility [syn: {strict}]
     3: incapable of adapting or changing to meet circumstances; "a
        rigid disciplinarian"; "an inflexible law"; "an unbending
        will to dominate" [syn: {inflexible}, {unbending}]
     4: fixed and unmoving; "with eyes set in a fixed glassy stare";
        "his bearded face already has a set hollow look"- Connor
        Cruise O'Brien; "a face rigid with pain" [syn: {fixed}, {set}]
     5: designating an airship or dirigible having a form maintained
        by a stiff unyielding frame or structure [ant: {nonrigid}]