Yet a great many processes depending on such research are sought for with complete secrecy until the stage at which patents can be taken out. (J.D. Bernal "Secrecy in Industry," in L.G. Alexander, New Concept English, Book 4; emphasis mine)
How is the phrase "a great many processes" grammatical? Shouldn't one use the indefinite article "a" only before a singular noun (while here it is the plural "processes")?