Sentence:  Spenser's] stile was in his own time allowed to be vicious, so <WSD>darkened</WSD> with old words and peculiarities of phrase, and so remote from common use, that "Johnson" boldly pronounces him to have written no language. 
Meaning of the word marked with <WSD> tags:  To cloud, obscure, or perplex; to render less clear or intelligible.