tantum

Tantum is a Latin word meaning "only, merely" or "so much," used primarily as an adverb to limit a statement. In classical Latin it functions as an indeclinable adverb and is often paired with negation in the phrase non tantum sed etiam, meaning not only but also, to emphasize contrast. It can also occur in phrases that translate roughly as "that much" or "as much," serving as a quantitative modifier in some contexts, though it is chiefly adverbial.

In ecclesiastical Latin, tantum is well known through the liturgical lyric Tantum Ergo Sacramentum, attributed to Thomas Aquinas. The opening lines, "Tantum ergo Sacramentum veneremur cernui," have been widely sung in Catholic worship and have given the term lasting prominence in religious Latin.

Etymologically, tantum derives from tantus "so great" or "such," sharing roots with modern Romance languages. The word retains its function as an indeclinable particle in Latin texts and continues to appear in scholarly discussions of Latin grammar and medieval and liturgical Latin.