Schaff's Bible Dictionary
AP'PLES, AP'PLE - TREE (Hebrew, breathing forth). Song of Solomon 2:3-5; Song of Solomon 7:8; Song of Solomon 8:5; Joel 1:12. Spoken of in the Scriptures as excellent "among the trees of the wood," of pleasant shadow, with sweet, beautiful, and fragrant fruit. The Hebrew word, by its meaning, is thought to emphasize the latter property. The apple proper is rare in Syria, and its fruit is inferior. Writers have urged the citron, orange, quince, and apricot as the trees meant. The fruit of the latter two alone is specially aromatic, and of these the quince is not sweet in taste.
" The expression of Solomon just referred to, Prov 25:11, is also supposed to compare fruit in silver baskets, or salvers curiously wrought like basket-work, and perhaps representing animals or landscapes, to seasonable advice wisely and courteously administered. Apple of the Eye (Hebrew, little man, or pupil of the eye). Prov 7:2; Zech 2:8. Apple here represents an entirely different word from the word of the preceding topic, meaning the front and most sensitive part of the organ of vision. The same figure is used, Deut 32:10 and Ps 17:8, to denote the most complete protection and security.
And in Lam 2:18 the phrase ''apple of thine eye" is figuratively used for tears.