The Collaborative International Dictionary of English v.0.48:
Sublingual \Sub*lin"gual\, a. [Pref. sub + lingual: cf. F. sublingual.] (Anat.) (a) Situated under the tongue; as, the sublingual gland. (b) Of or pertaining to the sublingual gland; as, sublingual salvia. [1913 Webster]WordNet (r) 3.0 (2006):
sublingual adj 1: beneath the tongue