Middle English pinen "cause to starve" (c. 1300), from Old English pinian "to torture, torment, afflict, cause to suffer," from *pīn (n.) "pain, torture, punishment," from a general Germanic word (compare Middle Dutch pinen, Old High German pinon, German Pein, Old Norse pina), all possibly ultimately from Latin poena "punishment, penalty" (see penal). If so, the Latin word probably came into Germanic with Christianity.
The intransitive sense of "to languish, waste away, be consumed with grief or longing," the main modern meaning, is recorded from early 14c., via the Middle English intransitive senses of "endure penance, torment oneself; endure pain, suffer." Related: Pined; pining.
"withering, liable to decay, ephemeral," 1727, from Latin marcescentem (nominative marcescens), present participle of marcescere "to wither, languish, droop, decay, pine away," inchoative of marcere "to wither, droop, be faint," from Proto-Italic *mark-e-, from PIE root *merk- "to decay" (source also of Sanskrit marka- "destruction, death;" Avestan mareka- "ruin;" Lithuanian mirkti "become weak," merkti "to soak;" Ukrainian dialect morokva "quagmire, swamp," Middle High German meren "dip bread into water or wine," perhaps also Middle Irish mraich, Welsh brag "a sprouting out; malt").