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今 supplies the sound — jīn shifting to tān, an unusual k-/t- alternation rooted in Old Chinese consonant clusters that left modern doublets like
含 hán /
贪 tān.
今's 'now' meaning has no role here. The phonetic family is small but tight:
含 contain,
念 think-of,
琴 zither — all jin or yin-readers.