This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
稹 combines 禾 (grain) with 真, which likely contributes the sound. The exact historical development is uncertain, and the character is rare in modern Japanese.
With 禾 (grain) beside 真 (truth/reality), you might imagine a dense, thick growth of grain that looks truly abundant. This ties to the kun-reading しげ.る (to grow thick), but the kanji itself has no established English meaning.
For シン, picture the grain 禾 growing so thick that it forms a dense, true 真 forest: the scene is a shin (シン) deep thicket, where shin sounds like the reading.