sad, melancholy, grieving, mourn
惙 centers on a heavy, sorrowful state of mind: sadness, melancholy, grieving, or mourning. The meanings all point to deep emotional pain.
惙 combines 忄 (heart/mind) with 叕, which likely contributes the sound and may relate to joining or connecting, but the exact historical development of the compound is uncertain.
The heart radical 忄 beside 叕 suggests a heart that is tied up or entangled in sorrow. Picture your heart being bound by threads of grief, leaving you sad and mourning.
For テツ, imagine a sad person whose heart is heavy as iron: tetsu (鉄, iron) -> テツ, and the weight of iron matches the weight of melancholy.