mud·stone 
(mŭdstōn′)
(mŭdstōn′)n.
A fine-grained, dark gray sedimentary rock, formed from silt and clay and similar to shale but without laminations.
- nonprofit
- nonproliferation
- nonproprietary name
- nonpros
- non prosequitur
- nonreader
- nonrecombinant
- nonrecoverable
- non-REM sleep
- nonrenewable
- nonrepresentational
- nonresidence
- nonresidency
- nonresident
- nonresistance
- nonresistant
- nonrestrictive
- nonreturnable
- nonrigid
- nonscheduled
- nonsectarian
- nonsectarianism
- nonsedating
- nonself
- nonsense