This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 阷 is uncertain. It combines ⻖ (mound, hill) with 正 (correct, straight), but the original meaning and component relationship are unclear.
With no clear meaning, picture a mound (⻖) that is perfectly straight (正) — perhaps a leveled hill, but the true meaning remains a mystery.
For テイ, imagine a tea (ティー) party on a straight mound: tea -> テイ, though the kanji's meaning is uncertain.