rigid

Short definition from Wiktionary

Adjective

1. 1
   Stiff, rather than flexible.
2. 2
   Having inflexible thoughts, opinions, or beliefs.
3. 3
   Fixed, rather than moving.
4. 4
   Rigorous and unbending.
5. 5
   Uncompromising.

Noun

1. 1
   An airship whose shape is maintained solely by an internal and/or external rigid structural framework, without using internal gas pressure to stiffen the vehicle (the lifting gas is at atmospheric pressure); typically also equipped with multiple redundant gasbags, unlike other types of airship.
2. 2
   A bicycle with no suspension system.