Significatio vocis trietericus | Babel Free

Definitiones

1. of three years
   adjective, declension-1, declension-2
2. biennial; i.e., according to Roman timekeeping, inclusive of the years before and after
   adjective, declension-1, declension-2

Exempla

“… quālīs commōtīs excitā sacrīs Thȳias, ubi audītō stimulant trietērica Bacchō”

… excited by the sorts of sacred objects shaken by Thyia, [as] when [such sounds are] heard they incite Bacchus’ biannual orgies, and Mount Cythaeron harkens with cries in the night.

Gradus CEFR