This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 旲 is uncertain. It visually combines 日 (sun) and 大 (big), but the original meaning and component relationship are unclear.
The kanji looks like a big sun (日 over 大), but its meaning is unclear. Imagine a giant sun casting a shadow, hinting at the reading ひかげ (shade), though the meaning remains uncertain.
For タイ, picture a big sun (日 over 大) wearing a tie: tie -> タイ, even though the kanji's meaning is uncertain.