c. 1200, "decent, suitable, proper to the time, place, circumstances, or persons;" late 14c., "handsome, fair, graceful, pleasing in appearance" (of a man, woman, or thing), probably from Old English cymlic "lovely, splendid, finely made," from cyme "exquisite, glorious, delicate," which is apparently from West Germanic *kumi- "delicate, feeble" (source also of Old High German chumo "with difficulty," chumig "weak, delicate;" German kaum "hardly, scarcely"). OED compares the sense range of nice.
Or perhaps the modern word is from Middle English bicumelic (c. 1200) "suitable, exquisite," literally "becomely" (compare becoming). If this is not the source, it at least influenced the vowel. Related: Comelily; comeliness.