HIGGAION (hĭ-gā'yŏn, Heb. higgāyôn). A musical term in Ps.9.16, probably referring to the “solemn sound” (so 92:3 kjv) of harp music that was to be played at that point.

HIGGAION (הִגָּיֹ֣ון, talk or playing of instrument, Ps 92:4; Lam 3:62; thinking or planning, Ps 19:14). This Heb. word is used only four times in the OT. It occurs in Ugaritic as hgg with the meaning “to utter.” The word can basically be divided into two groups of meaning: the first has to do with sounds (either whispering or the playing of a stringed instrument); the second has to do with the process of planning or meditation. (See also Music; Musical Instruments.)

International Standard Bible Encyclopedia (1915)

hi-ga’yon, hi-gi’-on (higgayon): The meaning of this word is uncertain. Two interpretations are possible; the one based on an allied Arabic root gives "a deep vibrating sound," the other derived from the Greek versions of Ps 9:16, where we read higgayon Celah, takes it to mean an instrumental interlude.