This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 夳 is uncertain. It visually combines 大 (big) and 二 (two), but this may not reflect its original formation.
With no clear meaning, picture 大 (big) over 二 (two) as a big number two, but its use is obscure.
For タイ, imagine a tie (ネクタイ) with a big '2' printed on it: tie -> タイ, and the big 大 over 二 shape reminds you of the reading.