Mark in the intersection of 58-Across and 43-Down

• Façade part
• Mark under a letter c
• French "c" feature, maybe
• Literally, "little z," in old Spanish
• Diacritical mark under a 'c'
• Mark under a consonant
• Mark indicating a softened consonant
• Mark suggesting a 'c' should be pronounced an 's'
• French diacritical mark

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
c.1600, from Spanish cedilla , zedilla , literally "little z," from a Latin-like diminutive of Greek zeta "the letter 'z'." The mark (formerly also used in Spanish) was derived from that letter and indicates a "soft" sound in letters in positions where ...