This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 圠 is uncertain. It combines 土 (earth) with a hook-like element, but the original function is unclear.
The kanji looks like earth 土 with a small hook or barb attached. Without a clear meaning, it may help to remember it as an obscure earth-related character.
For アツ, imagine pressing a hook into the earth with a hot iron: the hiss of heat sounds like 'atsu' (アツ).