alike, truth
洵 centers on the idea of something being genuinely as it appears: truthful, sincere, or alike in the sense of being true to a standard. The meanings 'alike' and 'truth' connect through the concept of faithful correspondence.
洵 combines 氵 (water) with 旬, which likely contributes the sound. The exact historical development of the meaning 'truth' or 'alike' from these components is uncertain.
Water 氵 reflects things truly, like a mirror. The right side 旬 suggests a period of time, but together picture water that always shows the true, alike image over time.
For ジュン, imagine a truthful person named June who always tells the truth: June -> ジュン, and her honesty is as clear as water.