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Fausset's Bible Dictionary [1]

( Psalms 84:6). "Valley of Baca". i.e. "the vale of tears" (compare Bochim,  Judges 2:5, "the place of weepers.") The Hebrew form in  Psalms 84:6 means "mulberry trees." The Hebrew poet, by a play on the name, refers to the similarly sounding word for "tears." The Baca (mulberry) trees delight in a dry valley; such as the ravine of Hinnom below mount Zion, where the bacaim (mulberry trees) are expressly mentioned on the ridge separating the valley of Rephaim from that of Hinnom ( 2 Samuel 5:23).

Abulfadl says Βaca is the Arabic for a balsam-like shrub with round large fruit, from which if a leaf be plucked a tear-like drop exudes. As the valley of Baca represents a valley of drought spiritually and dejection, where the only water is that of "tears," so the pilgrim's "making it a well" (by having "his strength in Jehovah") symbolizes ever flowing comfort and salvation ( John 4:14;  Isaiah 12:3; compare  Psalms 23:4). David, to whom Psalm 84 refers, passed through such a valley of drought and tears when, fleeing from Absalom, he went up mount Olivet weeping as he went.

Smith's Bible Dictionary [2]

Ba'ca. (Weeping). The Valley Of Baca . A valley in Palestine, through which the exiled Psalmist sees, in vision, the pilgrims passing in their march towards the sanctuary of Jehovah at Zion.  Psalms 84:6. That it was a real locality is most probable from the use of the definite article before the name.

The rendering of the Targum is Gehenna , that is, the Ge-Hinnom or ravine below Mount Zion. This locality agrees well with the mention of balsam (Authorized Version, "mulberry") trees in  2 Samuel 5:23.

People's Dictionary of the Bible [3]

Baca ( Bâ'Ca ), Weeping, Lamentation. A valley in Palestine, probably sterile.  Psalms 84:6 A. V.; but the R. V. translates it "weeping." The pilgrim-journeys to Jerusalem are here described. Those who so go up, "passing through the valley of weeping, make it a spring," I.E., the sterile land becomes to them a watered valley. The plural of this word is rendered "mulberry trees" in  2 Samuel 6:23;  1 Chronicles 14:14-15.

American Tract Society Bible Dictionary [4]

Tears, or weeping,  Psalm 84:6 . It is not necessary to understand here that there was really a valley so called. The psalmist, at a distance from Jerusalem, is speaking of the happiness of those who are permitted to make the usual pilgrimages to that city in order to worship Jehovah in the temple: they love the ways which lead thither; yea, though they must pass through rough and dreary paths, even a vale of tears, yet such are their hope and joy of heart, that all this is to them as a well-watered country, a land crowned with the blessings of early rain.

Hawker's Poor Man's Concordance And Dictionary [5]

We meet with this word but once in Scripture, and that is in the book of Psalms, ( Psalms 84:6) The meaning of it seems to be weeping; though some consider it as referring to the mulberry tree.

Wilson's Dictionary of Bible Types [6]

 Psalm 84:6 (b) The word means "weeping," a picture of a dry, dead church or community which becomes spiritually awakened and enriched by the ministry of a Spirit-filled servant of GOD.

Holman Bible Dictionary [7]

 Psalm 84:6

Kitto's Popular Cyclopedia of Biblial Literature [8]

Ba´ca and Becaim occur, the first in  Psalms 84:6, 'Who passing through the valley of Baca make it a well; the rain also filleth the pools;' the second in  2 Samuel 5:23-24, and in  1 Chronicles 14:14-15, 'And let it be, when thou hearest the sound of a going in the tops of the mulberry trees, that thou shalt bestir thyself.' Neither the mulberry nor the pear-tree, considered by some to be the baca of the Scriptures, satisfies translators and commentators, because they do not possess any characters particularly suitable to the above passages.

It is evident that the tree alluded to, whatever it is, must be common in Palestine, must grow in the neighborhood of water, have its leaves easily moved, and have a name in some of the cognate languages similar to the Hebrew Baca. The only one with which we are acquainted answering to these conditions is that called bak by the Arabs, or rather shajrat al-bak—that is, the fly or gnat tree.

As it appears to us sufficiently clear that the bak-tree is a kind of poplar, and as the Arabic 'bak' is very similar to the Hebrew 'Baca,' so it is probable that one of the kinds of poplar may be intended in the above passages of Scripture. And it must be noted that the poplar is as appropriate as any tree can be for the elucidation of the passages in which baca occurs. For the poplar is well known to delight in moist situations, and Bishop Horne, in his Comm. on Psalms 84, has inferred that in the valley of Baca the Israelites, on their way to Jerusalem, were refreshed by plenty of water. It is not less appropriate in the passages in II Samuel and I Chronicles, as no tree is more remarkable than the poplar for the ease with which its leaves are rustled by the slightest movement of the air; an effect which might be caused in a still night even by the movement of a body of men on the ground, when attacked in flank or when unprepared. That poplars are common in Palestine may be proved from Kitto's Palestine, i. 114 'Of poplars we only know, with certainty, that the black poplar, the aspen, and the Lombardy poplar grow in Palestine. The aspen, whose long leaf-stalks cause the leaves to tremble with every breath of wind, unites with the willow and the oak to overshadow the watercourses of the Lower Lebanon, and, with the oleander and the acacia, to adorn the ravines of southern Palestine: we do not know that the Lombardy poplar has been noticed but by Lord Lindsay, who describes it as growing with the walnut-tree and weeping-willow under the deep torrents of the Upper Lebanon.'

International Standard Bible Encyclopedia [9]

bā´ka בּכא , bakha' ̌ : In the King James Version in  Psalm 84:6 , where the Revised Version (British and American) has "the valley of Weeping," with a marginal variant which is best put in the form, "the valley of the balsam-trees." The word is elsewhere used only in the duplicated account of one of David's battles ( 2 Samuel 5:23 ,  2 Samuel 5:24;  1 Chronicles 14:14 ,  1 Chronicles 14:15 ). There the translation is "the mulberry trees," with "the balsam-trees" in the margin in the Revised Version (British and American). Conjecturally the word is, by variant spelling, of the stem which denotes weeping; the tree is called "weeper" from some habit of the trickling of its gum or of the moisture on it; the valley of weeping is not a geographical locality, but a picturesque expression for the experiences of those whose strength is in Yahweh, and who through His grace find their sorrows changed into blessings.