タイ, か.える, か.え, か.わる, かえ
exchange, spare, substitute, per-
JLPT2 G7 S12 F979
The relevant seal inscription form is an element# doubling 夫 and indicating "stand in alignment" (compare 輦) + 曰 say/speech indicator → circular group of people taking turns speaking → *relieve/succeed another*; *replace*; *exchange*; *substitute for* → *alternate*; *change* → *a spare*; *another* (helping of food etc.). Later, 曰 was replaced by 日.
[Full Kanji Etymology List]