From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

Willow ( ‘ăr âbîm ,   Leviticus 23:40 ,   Job 40:22 ,   Psalms 137:2 ,   Isaiah 15:7;   Isaiah 44:4 [cf. Arab. [Note: Arabic.] gharab ‘willow’ or ‘poplar’]; tsaph-tsâphâh ,   Ezekiel 17:5 [cf. Arab [Note: Arabic.] , safsaf ‘the willow’]). Most of the references are to a tree growing beside water, and apply well to the willow, of which two varieties, Salix fragilis and S. alba , occur plentifully by watercourses in the Holy Land. Some travellers consider the poplar , especially the willow-like Populus euphratica , of the same Nat. Ord. ( SalicaceÅ“ ) as the willows, more probable. Tristram, without much evidence, considered that tsaphtsâphâh might be the oleander , which covers the banks of so many streams.

E. W. G. Masterman.

Webster's Dictionary [2]

(1): ( v. t.) To open and cleanse, as cotton, flax, or wool, by means of a willow. See Willow, n., 2.

(2): ( n.) A machine in which cotton or wool is opened and cleansed by the action of long spikes projecting from a drum which revolves within a box studded with similar spikes; - probably so called from having been originally a cylindrical cage made of willow rods, though some derive the term from winnow, as denoting the winnowing, or cleansing, action of the machine. Called also willy, twilly, twilly devil, and devil.

(3): ( n.) Any tree or shrub of the genus Salix, including many species, most of which are characterized often used as an emblem of sorrow, desolation, or desertion. "A wreath of willow to show my forsaken plight." Sir W. Scott. Hence, a lover forsaken by, or having lost, the person beloved, is said to wear the willow.

American Tract Society Bible Dictionary [3]

A very common tree, which grows in marshy places,  Job 40:22   Isaiah 44:4 , with a leaf much like that of the olive. God commanded the Hebrews to take branches of the handsomest trees, particularly of the willows of the brook, and to bear them in their hands before the Lord, as a token of rejoicing, at the feast of Tabernacles,  Leviticus 23:40 .

The "weeping willow," memorable in connection with the mourning Hebrew captives,  Psalm 137:2 , is a native of Babylonica. The "book of the willows,"  Isaiah 15:7 , on the southern border of Moab, flows into the southeast extremity of the Dead Sea.

Morrish Bible Dictionary [4]

ereb. Supposed to be the Salix Babylonica. Its boughs were used at the Feast of Tabernacles, a season of joy; but at the captivity and since, it is a symbol of sorrow. It was on such that the captives hung their harps when in captivity, of which the Psalmist spoke prophetically.  Leviticus 23:40;  Job 40:22;  Psalm 137:2;  Isaiah 15:7;  Isaiah 44:4 . In  Ezekiel 17:5 the word is tsaphtsaphah, supposed by some to be the Arabic safsâf, a willow or osier which grows by the water.

King James Dictionary [5]

WILLOW, n. L. A tree of the genus Salix. There are several species of willow, the white, the black, the purple or red, the sallow, and the broad leaved willow, &c. A species called the weeping willow, has long and slender branches which droop and hang downward, the Salix Babylonica.

Holman Bible Dictionary [6]

 Leviticus 23:40 Psalm 137:1-4Plants In The Bible

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [7]

Copyright StatementThese files are public domain. Bibliography InformationMcClintock, John. Strong, James. Entry for 'Willow'. Cyclopedia of Biblical, Theological and Ecclesiastical Literature. https://www.studylight.org/encyclopedias/eng/tce/w/willow.html. Harper & Brothers. New York. 1870.