首楞嚴義疏注經 5.153

5.153

亦云優波尼殺曇，此言近少，或云塵性，謂微塵是色之近少分也。因觀不淨白骨微塵，故以為名。由多貪欲，故作此觀以為對治。復了色塵本如來藏，故云悟諸色性。二、正陳悟旨，二：一、觀成得道。

Also written as Upaniṣad [優波尼殺曇], which here is translated as 'near-less' [kāraṇa / sūkṣma], or called 'dust nature,' meaning that subtle dust (paramāṇu) is the near-less [minimal] part of form. Because he contemplated impurity, white bones, and subtle dust, he took this as his name. Since he had much greed and desire, he undertook this contemplation as an antidote. Furthermore, he realized that the dust of form is originally the tathāgatagarbha, hence he says 'awakening to the nature of all form.' Second, directly setting forth the purport of his awakening, in two [parts]: first, the contemplation succeeded and he attained the Way.