Acceptable for a long time:
— Time-honored customs.

synonym: time-honoured.

Roget 928: respecting etc. v.; respectful, deferential, decorous, reverential, obsequious, ceremonious, bareheaded, cap in hand, on one's knees; prostrate etc. (servile) 886.    respected etc. v.; in high esteem, in high estimation; time-honored, venerable, emeritus.    ... show more

Roget 124: old, ancient, antique; of long standing, time-honored, venerable; elder, eldest; firstborn.    prime; primitive, primeval, primigenous^†; paleolontological, paleontologic, paleoanthropological, paleoanthropic^†, paleolithic, primordial, primordinate^†; aboriginal etc. (beginning) 66; diluvian^†, antediluvian; protohistoric^†; prehistoric; antebellum, colonial, precolumbian; patriarchal, preadamite^†; paleocrystic^†; fossil, paleozoolical, paleozoic, preglacial^†, antemundane^†; archaic, classic, medieval, Pre-Raphaelite, ancestral, black-letter.    immemorial, traditional, prescriptive, customary, whereof the memory of man runneth not to the whereof the memory of man runneth not to the contrary; inveterate, rooted.    antiquated, of other times, rococo, of the old school, after-age, obsolete; out of date, out of fashion, out of it; stale, old-fashioned, behind the age; old-world; exploded; gone out, gone by; passe, run out; senile etc. 128; time worn; crumbling etc. (deteriorated) 659; secondhand.    old as the hills, old as Methuselah, old as Adam^†, old as history.    [geological eras (list, starting at given number of years bp)] Archeozoic [5,000,000,000], Proterozoic [1,500,000,000], Paleozoic [600,000,000], Mesozoic [220,000,000], Cenozoic [70,000,000]. [geological periods] Precambrian, Cambrian [600,000,000], Ordovician [500,000,000], Silurian [440,000,000], Devonian [400,000,000], Mississippian [350,000,000], Pennsylvanian [300,000,000], Permian [270,000,000], Triassic [220,000,000], Jurassic [180,000,000], Cretaceous [135,000,000], Tertiary [70,000,000], Paleogene [70,000,000], Neocene [25,0000,000], Quaternary [1,000,000]. [geological epochs (list, starting at 70,000,000 years bp)] Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Recent.    ... show more

Honored because of age or long usage:
— Time-honored institutions.

synonym: time-honoured.