• WordNet 3.6
    • n labdanum a soft blackish-brown resinous exudate from various rockroses used in perfumes especially as a fixative
    • n labdanum a dark brown to greenish oleoresin that has a fragrant odor and is used as a fixative in perfumes; obtained as a juice from certain rockroses
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Webster's Revised Unabridged Dictionary
    • n Labdanum (Bot) See Ladanum.
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Century Dictionary and Cyclopedia
    • n labdanum See ladanum.
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Chambers's Twentieth Century Dictionary
    • Labdanum . See Ladanum.
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In literature:

Then take the best labdanum, benjoin, with storaxes, ambergris, civet, and musk.
"Folk-lore of Shakespeare" by Thomas Firminger Thiselton-Dyer
You may try a strong ethereal or alcoholic solution of benzoin, tolu, storax, olibanum or labdanum.
"Scientific American, Vol. XXXIX.--No. 24. [New Series.], December 14, 1878" by Various