出典:Wiktionary
Before 1000 CE - From Middle English grinnen, from 古期英語 grennian, of Germanic origin and probably related to groan. Compare to Old High German grennan (“to mutter”) and Danish grine (“to show one's teeth, to laugh”)
grin (三人称単数 現在形 grins, 現在分詞 grinning, 過去形および過去分詞形 grinned)
Unknown.