rigid

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Not flexible or pliant; stiff.
2. adj. Not moving; fixed.
3. adj. Marked by a lack of flexibility; rigorous and exacting: "We have watered down a rigid training . . . until we now have an educational diet in many of our public high schools that nourishes neither the classes nor the masses” ( Agnes Meyer).
4. adj. Scrupulously maintained or performed: rigid discipline. See Synonyms at stiff.

Century Dictionary and Cyclopedia

1. Stiff; not pliant or easily bent; not plastic or easily molded; resisting any change of form when acted upon by force; hard.
2. Not easily driven back or thrust out of place; unyielding; firm.
3. Not easily wrought upon or affected; inflexible; hence, harsh; severe; rigorous; rigorously framed or executed: as, a rigid sentence; rigid criticism.
4. Strict in opinion, conduct, discipline, or observance; uncompromising; scrupulously exact or exacting: as, a rigid disciplinarian; a rigid Calvinist.
5. Stiff in outline or aspect; harsh; hard; rugged; without smoothness, softness, or delicacy of appearance.
6. Sharp; severe; bitter; cruel.
7. In dynamics: Absolutely incapable of being strained.
8. Resisting stresses.
9. Synonyms and Severe, Rigorous, etc. (see austere), inflexible, unbending, unyielding.

Wiktionary

1. adj. Stiff, rather than flexible.
2. adj. Fixed, rather than moving.
3. adj. Rigorous and unbending.
4. adj. Uncompromising.

GNU Webster's 1913

1. adj. Firm; stiff; unyielding; not pliant; not flexible.
2. adj. Hence, not lax or indulgent; severe; inflexible; strict.

WordNet 3.0

1. adj. incapable of compromise or flexibility
2. adj. fixed and unmoving
3. adj. designating an airship or dirigible having a form maintained by a stiff unyielding frame or structure
4. adj. incapable of adapting or changing to meet circumstances
5. adj. incapable of or resistant to bending