tranquil

Adjective

Synonyms: placid quiet still smooth unruffled calm unagitated serene

WordNet 3.0

Adjective (2)

(of a body of water) free from disturbance by heavy waves“a ribbon of sand between the angry sea and the placid bay”“the quiet waters of a lagoon”“a lake of tranquil blue water reflecting a tranquil blue sky”“a smooth channel crossing”“scarcely a ripple on the still water”“unruffled water”Synonyms: placid quiet still smooth unruffled
not agitated; without losing self-possession“spoke in a calm voice”“remained calm throughout the uproar”“he remained serene in the midst of turbulence”“a serene expression on her face”“she became more tranquil”“tranquil life in the country”Synonyms: calm unagitated serene

Webster's Dictionary (GCIDE)

Tranquil \Tran"quil\, a. [L. tranquillus; probably fr. trans across, over + a word akin to quietus quiet: cf. F. tranquille. See Quiet.] Quiet; calm; undisturbed; peaceful; not agitated; as, the atmosphere is tranquil; the condition of the country is tranquil. [1913 Webster]

A style clear, tranquil, easy to follow. --De Quincey. [1913 Webster] Tranquilization

Free On-line Dictionary of Computing

TRANQUIL

1966.ALGOL-like language with sets and other extensions, for the Illiac IV. "TRANQUIL: A Language for an Array Processing Computer", N.E. Abel et al, Proc SJCC 34 (1969).