The earliest oracle bone inscriptions show 木 (“tree”) with dots around it representing flames – sacrifice with firewood. In some oracle bone inscriptions, 火 (“fire”) was added to emphasize the fire used in the sacrifice.
In the bronze inscriptions, 呂 (OC *ɡ·raʔ) was often added as a phonetic component, as seen in 寮 (OC *reːw) and 潦 (OC *reːwʔ, *reːws). This component may have been the basis of the 日 component found in late bronze inscriptions and in the seal script.
Shuowen interprets the character as 眘(“serious”) + 火(“fire”).