slacken, loosen, relax, lessen, be moderate, ease
緩 centers on reducing tension or intensity: making something slack, loose, or relaxed, and by extension lessening pressure or being moderate.
緩 combines 糸 (thread) with 爰, which likely contributes the sound and the idea of pulling or stretching. The overall sense is of a thread being loosened or relaxed.
The left side is thread 糸, and the right side 爰 looks like a hand pulling something. Imagine pulling a thread to loosen a tight knot: the tension slackens and relaxes.
For カン, picture a can of soda that has been left open and gone flat—the fizz has slackened and relaxed. Can -> カン, and the thread-like bubbles have eased away.
loose
relief; mitigation; alleviation; relaxation (of restrictions, tensions, etc.); easing; softening
loose; slack
somewhat loose
to become loose; to slacken (e.g. rope)
shock absorption; buffer action; cushioning; buffer
to loosen; to slacken
relaxation (e.g. of muscles); becoming flaccid
high and low speed; fast and slow; pace; tempo
slack; looseness; play
slow; sluggish; dull; slack; inactive
unhurriedly; leisurely; slowly; relaxedly; taking one's time
going slowly
to weaken (of willpower, solidarity, etc.); to lose one's edge; to become less tense; to become lax (of discipline, rules, etc.)
(when) danger threatens; should an emergency occur
partial relaxation; partial easing
dynamic buffering
simple buffering
to smile; to crack a smile
looking cool and collect; with an air of perfect composure