The Poetical Books.
... sung. "Negiloth" means stringed instruments; it indicates the kind of
accompaniment with which the psalm was to be sung. "Nehiloth ...
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Supposed to mean flutes or wind instruments; found only in the title of the fifth Psalm, which is addressed, to the leader of this class of instruments, as though intended to be sung with this accompaniment only.

Negiloth

Nehiloth