This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
緂 combines 糸 (thread) with 炎 (flame). The exact historical development is uncertain, but it likely relates to a type of fabric or a vivid color, given the kun reading あざやか (vivid).
Imagine a vivid flame-colored thread: 糸 (thread) beside 炎 (flame) suggests a bright, striking fabric.
For タン, picture a tan-colored thread catching fire: tan -> タン, and the flame makes the thread vivid.