ཡ་མ་བརླ།

The word ya ma brla (“essence-less, non-essential, hollow” or “fickle,” “unreliable”) seems to have an etymology especially because of its similarity with ya ma zung. The word is recorded in the Bod rgya (ss.v. ya ma brla & stong pa) and in Jäschke 1881: s.v. Is Jäschke suggesting ya ma la and if so what does it mean? The meaning (albeit not the etymology) of the word seems to be clear also in the following statement by Rong-zom-pa: ’o na sku dang ye shes kyi dkyil ’khor de dag kyang gsob ya ma brla sgyu ma lta bu yin pas | don gyis (sic) dgos pa ci yang med zhig yin nam zhe na | (RZ 1: 171). But what could be its etymology? Could it be something like “neither upper [part of the body] nor thigh (i.e. lower part of the body) hence in reality “nothing,” “non-substantial,” or, “non-essential”?