This generally means “massive.” Obviously, it comes from the root of Cyclops, the monster from Greek and Roman mythology. “Cyclops” means “round eye” which was used to describe a giant creature with one eye.
The word seems to be common masonry industry, to refer to stonework done with large stones. The Cyclops of legend were supposedly masons of a sort – having built massive walls out of stones.
From Wordnik (which cites The Century Dictionary from the 1800s).
applied to an early style of masonry, sometimes imitated in later ages, constructed of stones either unhewn or more or less irregularly shaped and fitted together, usually polygonal, but in some more recent examples approaching regular horizontal courses, and often presenting joints of very perfect workmanship
Why I Looked It Up
H.P. Lovecraft uses the word a lot. He deals in “scary, big things,” and it’s one of his favorite words to describe stuff that should scare you.
From Call of Cthulhu, for example:
Behind the figure was a vague suggestion of a Cyclopean architectural background.
[…] Remains of Them, he said the deathless Chinamen had told him, were still to be found as Cyclopean stones on islands in the Pacific.
[…] He talked of his dreams in a strangely poetic fashion; making me see with terrible vividness the damp Cyclopean city of slimy green stone…