A crossbow was a projectile weapon that consisted of a bow mounted on a stock that shot arrows. A mechanism in the stock held the bow in its fully-drawn position, and the projectile was shot by pressing a trigger.
The Akaali Riaan threatened Captain Jonathan Archer and Trip Tucker with a small crossbow during their first encounter in 2151. A larger, wall-mounted crossbow was present in Garos' curio shop. (ENT: "Civilization")
Lieutenant Worf kept a crossbow in his quarters aboard the USS Enterprise-D. In 2369, Captain Jean-Luc Picard used this crossbow to help take back his ship from mercenaries who were planning on stealing trilithium resin. (TNG: "Starship Mine")