Lacking energy, enthusiasm, or liveliness.
Uncompromising.
Stiff, rather than flexible.
Fixed, rather than moving.
Rigorous and unbending.
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.
A bicycle with no suspension system.