-acy Look up -acy at Dictionary.com
word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin: 1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as. 2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus. 3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. Extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).