bamboo shoot
笋 centers on the young, edible shoot of bamboo that emerges from the ground.
笋 combines 竹 (bamboo) with 尹, which likely contributes a phonetic element. The character specifically denotes a bamboo shoot.
Bamboo 竹 above 尹: picture a bamboo shoot pushing up from the ground, with the lower part representing the emerging tip.
For ジュン, imagine a bamboo shoot growing in June: June -> ジュン, and the shoot appears in early summer.