The Sidicini (Ancient Greek Σιδικῖνοι) were one of the Italic peoples of ancient Italy. Their territory extended northward from their capital, Teanum Sidicinum (modern day Teano), along the valley of the Liri river up to Fregellae, covering around 3,000 square kilometres (1,200 square miles) in total. They were neighbors of the Samnites and Campanians, and allies of the Ausones and Aurunci. Their language was Oscan.
Oscan is an extinct Indo-European language of southern Italy. The language is in the Osco-Umbrian or Sabellic branch of the Italic languages. Oscan is therefore a close relative of Umbrian and South Picene.
Oscan was spoken by a number of tribes, including the Samnites, the Lucani, the Aurunci (Ausones), and the Sidicini. The latter two tribes were often grouped under the name "Osci". The Oscan group is part of the Osco-Umbrian or Sabellic family, and includes the Oscan language and three variants (Hernican, Marrucinian and Paelignian) known only from inscriptions left by the Hernici, Marrucini and Paeligni, minor tribes of eastern central Italy. Adapted from the Etruscan alphabet, the Central Oscan alphabet was used to write Oscan in Campania and surrounding territories from the 5th century BCE until at least the 1st century CE.