This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
愙 combines 客 (guest) and 心 (heart). The exact historical development is uncertain, but it may have originally expressed a respectful or cautious attitude, as suggested by the kun reading つつしむ (to be respectful/cautious).
A guest (客) with a heart (心) below: imagine a guest being extra careful and respectful, holding their heart in check.
For カク, picture a cautious guest knocking (カク) softly before entering, showing respect.