This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form visually combines 雨 (rain) with 鶴 (crane), but this may be a variant or a later compound rather than a direct historical derivation.
The kanji has no clear meaning, but visually it looks like a crane (鶴) under the rain (雨).
For カク, imagine a crane (鶴) calling out 'kaku' as it stands in the rain: kaku -> カク.