incapable of or resistant to bending; "a rigid strip of metal"; "a table made of rigid plastic"; "a palace guardsman stiff as a poker"
incapable of compromise or flexibility
designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
An idealized concept meaning something which does not deform under loading. In fact, all objects deform under loading, but in modelling it can be useful to idealize very stiff objects as rigid.
Not flexible or pliant; stiff
something that isn't flexible and won't bend