A suffix-like verb (commonly written in kana as しきる) that follows a verb stem to indicate that an action occurs repeatedly or continuously (e.g. 降りしきる: rain keeps falling).
夜半を過ぎても雨が降りしきっていた。
Even after midnight, the rain kept pouring.
冬は雪が降りしきる日が多い地域だ。
In winter it's a region with many days of continuous snowfall.
銃声が鳴りしきて町は不安に包まれた。
Gunshots kept sounding, and the town was wrapped in anxiety.
An archaic intransitive verb meaning to occur repeatedly or again and again; now largely literary or archaic.
昔、この地には疫病が頻ったと記録にある。
Records say that in old times epidemics occurred repeatedly in this area.
争いが頻りに起こり、村人は疲弊した。
Conflicts happened repeatedly and the villagers were exhausted.