The Collaborative International Dictionary of English v.0.48:

Tantra \Tan"tra\ (t[a^]n"tr[.a]; t[u^]n"tr[.a]), n. [Skr.]
   (Hinduism)
   A ceremonial treatise related to Puranic and magic
   literature; esp., one of the sacred works of the worshipers
   of Sakti. -- Tan"tric (t[a^]n"tr[i^]k), a.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Tantric
    adj 1: of or relating to Tantrism; "Tantric rituals" [syn:
           Tantric, Tantrik]