This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
闙 combines 門 (gate) with 啟 (open, begin). The exact historical development is uncertain, but it likely relates to opening a gate or door.
A gate 門 with 啟 inside suggests opening or beginning something behind a door, but the exact meaning is uncertain.
For ケイ, imagine a key (ケイ) opening the gate 門: key -> ケイ, and the gate swings open.