What is the X in X-mas?
Old English leaf "leaf of a plant; page of a book," from Proto-Germanic *laubaz (cf. Old Saxon lof, Old Norse lauf, Old Frisian laf, Dutch loof, Old High German loub, German Laub "foliage, leaves," Gothic lauf), perhaps from PIE *leup- "to peel off, break off" (cf. Lithuanian luobas, Old Church Slavonic lubu "bark, rind"). Extended 15c. to very thin sheets of metal (especially gold). Meaning "hinged flap on the side of a table" is from 1550s.
"to turn over (the pages of a book)," 1660s, from leaf (n.). The notion of a book page also is in the phrase to turn over a (new) leaf (1570s). Related: Leafed; leaved; leafing.
Old English læfan "to let remain; remain; have left; bequeath," from Proto-Germanic *laibijan (cf. Old Frisian leva "to leave," Old Saxon farlebid "left over"), causative of *liban "remain," (cf. Old English belifan, German bleiben, Gothic bileiban "to remain"), from root *laf- "remnant, what remains," from PIE *leip- "to stick, adhere;" also "fat."
The Germanic root has only the sense "remain, continue," which also is in Greek lipares "persevering, importunate." But this usually is regarded as a development from the primary PIE sense of "adhere, be sticky" (cf. Lithuanian lipti, Old Church Slavonic lipet "to adhere," Greek lipos "grease," Sanskrit rip-/lip- "to smear, adhere to." Seemingly contradictory meaning of "depart" (early 13c.) comes from notion of "to leave behind" (as in to leave the earth "to die;" to leave the field "retreat").
"permission," Old English leafe "leave, permission, license," dative and accusative of leaf "permission," from West Germanic *lauba (cf. Old Norse leyfi "permission," Old Saxon orlof, Old Frisian orlof, German Urlaub "leave of absence"), from PIE *leubh- "to care, desire, love, approve" (see love (n.)). Cognate with Old English lief "dear," the original idea being "approval resulting from pleasure." Cf. love, believe. In military sense, it is attested from 1771.
An appendage growing from the stem of a plant. Leaves are extremely variable in form and function according to species. For example, the needles of pine trees, the spines of cacti, and the bright red parts of the poinsettia plant are all leaves modified for different purposes. However, most leaves are flat and green and adapted to capturing sunlight and carbon dioxide for photosynthesis. They consist of an outer tissue layer (the epidermis) through which water and gases are exchanged, a spongy inner layer of cells that contain chloroplasts, and veins that supply water and minerals and carry out food. Some leaves are simple, while others are compound, consisting of multiple leaflets. The flat part of the leaf, the blade, is often attached to the stem by a leafstalk.
of a tree. The olive-leaf mentioned Gen. 8:11. The barren fig-tree had nothing but leaves (Matt. 21:19; Mark 11:13). The oak-leaf is mentioned Isa. 1:30; 6:13. There are numerous allusions to leaves, their flourishing, their decay, and their restoration (Lev. 26:36; Isa. 34:4; Jer. 8:13; Dan. 4:12, 14, 21; Mark 11:13; 13:28). The fresh leaf is a symbol of prosperity (Ps. 1:3; Jer. 17:8; Ezek. 47:12); the faded, of decay (Job 13:25; Isa. 1:30; 64:6; Jer. 8:13). Leaf of a door (1 Kings 6:34), the valve of a folding door. Leaf of a book (Jer. 36:23), perhaps a fold of a roll.