Antonym(s):

• transparent

Source(s):

CRYSTAL 2003474 (also "opaque rule")
TRASK 1996247-248 (also "opaque morpheme", "opaque rule", "opaque vowel")
NÖTH 1990243 (opaque word)
CHOMSKY 1981153
CRUSE 198639
HOCK 1986268
MATTHEWS 1997256
LONGACRE 1983327

• CRYSTAL, David. (2003) A Dictionary of Linguistics and Phonetics, 5th Ed Oxford: Blackwell.
• TRASK, R. L. (1996) A Dictionary of Phonetics and Phonology. London: Routledge. 
• NÖTH, Winfried. (1990) Handbook of Semiotics. Bloomington: Indiana University Press. 
• CHOMSKY, Noam. (1981) Lectures on Government and Binding. Dordrecht : Foris Publications.
• CRUSE, D.A. (1986) Lexical Semantics. Cambridge : Cambridge University Press.
• HOCK, Hans Henrich. (1986) Principles of Historical Linguistics. Berlin: Mouton de Gruyter.
• MATTHEWS, P.H. (1997) The Concise Oxford Dictionary of Linguistics. Oxford: Oxford University Press.
• LONGACRE, Robert E. (1983) The Grammar of Discourse. New York: Plenum Press.