threshold
閾 centers on a physical or figurative boundary point: a threshold that separates inside from outside, or a dividing line between states.
閾 combines 門 (gate) with 或, which likely contributes the sound and the idea of a bounded area, together suggesting the threshold of a gate.
The gate 門 encloses 或, a shape associated with a bounded region. Picture standing at the gate's threshold, the line between inside and outside.
For シキ, imagine a formal ceremony (式, しき) held at the threshold of a grand gate: 式 -> シキ, and the threshold marks the entrance to the ceremony.
threshold (amount, dose, etc.)
stimulus threshold; stimulus limen
difference threshold; differential limen
detection threshold
pain threshold
threshold of consciousness
threshold; limen
subliminal
subliminal
threshold stimulus; liminal stimulus