decorous

From the following:

Latin decōrus (“becoming, fitting, proper, suitable”) + English -ous (suffix adjectives denoting presence of a quality in any degree, typically an abundance). Decōrus is derived from decor (“elegrance, grace; charm beauty”) + -us (suffix forming adjectives); and decor is from decēre, the present active infinitive of decet (“to adorn; to be decent; to be proper or suitable”), ultimately from Proto-Indo-European *deḱ- (“to perceive; to take”).

Possibly also influenced by Late Latin decorōsus (“beautiful; elegant”), from decoris + -ōsus (suffix meaning ‘full of’ forming adjectives from nouns). Decoris is the genitive singular of decus (“beauty, grace, ornament, splendour; distinction, glory, honour”), from Proto-Indo-European *déḱos (“that which is proper”), from *deḱ- (see above).