This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 羍 is uncertain. It visually combines 大 (big) and 羊 (sheep), but the original meaning and component relationship are unclear.
Since the meaning is uncertain, picture a big sheep (大 over 羊) as a placeholder: a large sheep that defies easy description.
For タツ, imagine a big sheep named Tatsu: Tatsu -> タツ, a rare name for a rare kanji.
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