This is an old written form of 静 in the sense of quiet and calm.
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竫 is not used in modern Chinese; in classical texts it means quiet and at peace, an older equivalent of 静 (it also appears in 竫言, fabricated talk). It is 立 plus the phonetic 争, the same phonetic in 静 and 净.
立 is the stand radical, a person standing on the ground. Here it is the indexing element; the quietness sense comes from being still, standing settled and at rest.
