anthill, hill
垤 centers on a small mound of earth, specifically an anthill, but can refer to any small hill or raised earth.
垤 combines 土 (earth) with 至, which likely contributes the sound and may relate to the idea of reaching or arriving, suggesting earth that has been piled up to form a mound.
The left side 土 is earth, and the right side 至 looks like a mound with something on top. Picture an anthill: a small hill of earth built by ants.
For テツ, imagine a tiny anthill made of iron (鉄, てつ) filings: 鉄 -> テツ, and the iron filings form a small mound.