Definitions of rigid:

• adjective:   incapable of compromise or flexibility
• adjective:   incapable of or resistant to bending

  Example: "A rigid strip of metal"

• adjective:   designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
• adjective:   incapable of adapting or changing to meet circumstances

  Example: "A rigid disciplinarian"

• adjective:   fixed and unmoving

  Example: "A face rigid with pain"