Tsade (also spelled ṣade, ṣādē, ṣaddi, ṣad, tzadi, sadhe, tzaddik) is the eighteenth letter of the Semitic abjads, including Phoenician ṣādē , Hebrew ṣādi צ, Aramaic ṣāḏē , Syriac ṣāḏē ܨ, Ge'ez ṣädäy ጸ, and Arabic ṣād ص. Its oldest phonetic value is debated, although there is a variety of pronunciations in different modern Semitic languages and their dialects. It represents the coalescence of three Proto-Semitic "emphatic consonants" in Canaanite. Arabic, which kept the phonemes separate, introduced variants of ṣād and ṭāʾ to express the three (see ḍād, ẓāʾ). In Aramaic, these emphatic consonants coalesced instead with ʿayin and ṭēt, respectively, thus Hebrew ereṣ ארץ (earth) is araʿ ארע in Aramaic.

The Phoenician letter is continued in the Greek san (Ϻ) and possibly sampi (Ϡ), and in Etruscan 𐌑 Ś. It may have inspired the form of the letter tse in the Glagolitic and Cyrillic alphabets.

The corresponding letter of the Ugaritic alphabet is 𐎕 ṣade.

The letter is named "tsadek" in Yiddish, and Hebrew speakers often give it a similar name as well. This name for the letter probably originated from a fast recitation of the alphabet (i.e., "tsadi, qoph" → "tsadiq, qoph"), influenced by the Hebrew word tzadik, meaning "righteous person".