mittjährlichem
Mittjährlichem is the dative singular inflection of the German adjective mittjährlich, which denotes a semiannual rhythm—something that occurs roughly every six months or twice within a calendar year. The base form mittjährlich is formed from mittjähr- (mid-year) and -lich (an adjective suffix). In standard usage, the more common term for a six‑month interval is halbjährlich; mittjährlich appears chiefly in formal, technical, or legal language and can carry a nuance of focusing on the mid‑year period.
Grammatical note: mittjährlichem is used when the adjective precedes a masculine or neuter noun in the dative
Usage and nuance: mittjährlich stresses the half‑year mark or the general concept of a semiannual recurrence,