Boyd’s Bible Dictionary:
(drop). An oriental gum or spice, one of the components of the holy incense (Ex. 30:34).
Concise Bible Dictionary:
The word nataph signifies “a drop” and is so translated in Job 36:27. Hence stacte is doubtless a spice that oozes from a tree in drops: it formed a part of the holy incense (Ex. 30:34). The RV has in its margin “opobalsamum.” It is probably the gum from the storax tree, Styrax officinalis.
Jackson’s Dictionary of Scripture Proper Names:
a drop