[I, Ipr] ~ (at sb) smile broadly, so as to show the teeth, expressing amusement, foolish satisfaction, contempt, etc 露齿而笑（表示高兴﹑ 愚蠢的满足﹑ 轻蔑等）; 咧着嘴笑; 龇着牙笑: He grinned at me, as if sharing a secret joke. 他朝我龇牙一笑, 好像彼此会心领略一个笑话. * grin with delight 高兴得露齿一笑 * grin from ear to ear, ie very broadly 咧着大嘴笑. 
[Tn] express (sth) by grinning 露齿笑着表示（某事）: He grinned his approval. 他咧嘴一笑表示赞成. 
(idm 习语) grin and `bear it endure pain, disappointment, etc without complaining 毫无怨言地忍受痛苦﹑ 挫折等.> grin n act of grinning 露齿笑: a broad, foolish, silly, etc grin 咧着嘴的﹑ 愚蠢的﹑ 傻气的...一笑 * With a nasty grin on his face he took out a knife. 他狞笑着掏出了刀子.