variant of -able, occurring in words borrowed from Latin (credible; horrible; visible), or modeled on the Latin type (reducible).
Origin of -ible
< Latin -ibil(is) or -ībil(is), equivalent to -i- or -ī- thematic vowel + -bilis -ble
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suffix forming adjectives
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
suffix forming adjectives from verbs, borrowed in Middle English from Old French -ible and directly from Latin -ibilis; see -able.
Online Etymology Dictionary, © 2010 Douglas Harper