(1):

(vb. n.) Modification of tone for a rapid staccato effect by the performer's tongue, in playing a wind instrument, as a flute. In single tonguing only one kind of stroke is used, the tongue articulating a rapid "t;" in double tonguing, two strokes, as for "t" and "k," are alternated; in triple tonguing, "t, k, t," etc.

(2):

(p. pr. & vb. n.) of Tongue