/si dil"euh/ , n.
1. a mark (similar to a comma) placed under a consonant letter, as under c in French, in Portuguese, and formerly in Spanish, to indicate that it is pronounced /s/ , under c and s in Turkish to indicate that they are pronounced, respectively, /ch/ and /sh/ , or under t and s in Romanian to indicate that they are pronounced, respectively, /ts/ and /sh/ .
2. this mark used as a diacritic of arbitrary value in transliteration of words from non-Roman into Roman alphabetic characters.
[ 1590-1600; zedilla little z, equiv. to zed ( a ) ZED + -illa dim. suffix; the mark was so called from its original form ]