This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 冡 is uncertain. It visually contains 冖 (cover) and 豕 (pig), but the exact development is unclear.
With no clear meaning, picture a pig 豕 covered by a cloth 冖 with a line 一 across it — a mysterious, covered creature whose purpose is unknown.
For ボウ, imagine a bow (ボウ) tied around the covered pig, keeping it hidden. The bow sound cues ボウ.