incapable of or resistant to bending; "a rigid strip of metal"; "a table made of rigid plastic"; "a palace guardsman stiff as a poker"; "stiff hair"; "a stiff neck"
designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
characterized by forceful and energetic action or activity; "a vigorous hiker"; "gave her skirt a vigorous shake"; "a vigorous campaign"; "a vigorous foreign policy"; "vigorous opposition to the war"
strong and active physically or mentally; "a vigorous old man who spent half of his day on horseback"- W.H.Hudson
not changeable or subject to change; "a fixed and unchangeable part of the germ plasm"-Ashley Montagu; "the unchangeable seasons"; "one of the unchangeable facts of life"