What is the meaning of the term ‘‘Mayavadi’’? Is the term mentioned in any of the scriptures?
The earliest reference I can find is from the 8th century in Bhaskara's Bhasya on the Brahma Sutra. First see the remark made by Surendranath Dasgupta in the third volume of his History of Indian Philosophy:
Bhāskara argues against Śaṅkara as follows: the arguments that the upholder of māyā (māyāvādin) could adduce against those who believed in the reality of the many, the world, might be adduced against him also, in so far as he believes in monism (adraita). A person who hears the scriptures and philosophizes is at first under the veil of ignorance (avidyā); and, if on account of this ignorance his knowledge of duality was false, his knowledge of monism might equally for the same reason be considered as false. All Brahma-knowledge is false, because it is knowledge, like the knowledge of the world.
Note: Māyāvādī is the masculine nominative singular of the stem Māyāvādin (source).
Another book, “India & Beyond” details on Bhaskara’s definition and actually mentions the sourced reference:
Among the Vedāntins, Bhāskara (750-800) is probably one of the earliest critics against Śaṅkara. He called the Māyāvādin “one who depends on the doctrine of the Buddhist” (Bauddhamatāvalambin), and said that this position has been negated by the author of the Brahma Sūtra. (Bhāskara Brahmasūtra 2.2.29)
Afterwards, Yāmuna (918-1038), Rāmānuja (-1137), Madhva (1197–1276), Vallabha (1473-1531) and other Vedāntins severely criticized the Advaita Vedānta, pointing out that it is in essence nothing but a Buddhist doctrine.
Here is the relevant Sanskrit passage from Bhaskara’s Bhasya 2.2.29:
| ye tu bauddhamatāvalambino māyāvādinaste 'pyanena nyāyena sūtrakāreṇaiva nirastā veditavyāḥ |
So I guess it was Bhaskara who first coined and defined the term "Mayavadi" or "Mayavadin". Excluding of course potential non-extant earlier works.
Another scripture by Bhaskara using the word Mayavadin, is his commentary on the Bhagavadgita
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