stay的过去式为什么不是原形?跟stay的过去式相似的?

stay: 词根： st站立，树立，存在，坐落于to stand, set up 动词进行时： staying 过去式： stayed, staid 过去分词： stayed, staid v. 停留；停止，站住 n. 逗留，停留 名词 n. 逗留（时间）；停留（时间） visit (time) in a place · Your stay has been very short. 你呆的时间很短。 · I've very much enjoyed my stay here. 我在这里过得很愉快。 · Ed is back from a short stay with his uncle. 爱德在叔叔家呆了不多久，现在回来了。 不及物动词 vi. 停留 remain or continue in the same place · We stayed there for over three hours. 我们在那里呆了三个多小时。 · He stayed at home all day. 他整天呆在家里。 · Peter had to stay behind. 彼得得留下。 · She stayed at school until five o'clock. 她到五点才放学。 不及物动词 vi. 保持；持久 remain or continue in the same way; not change · My sister stayed single all along. 我姐姐一直是单身。 · Stay (keep)still a minute; I want to take your photograph. 稳定一会儿，我要给你照张相。 · Do you think this fine weather has come to stay? 你认为这种好天气会保持下去吗？ 不及物动词 vi. 暂住；耽搁 be a guest for a time He was staying at the Ritz(Hotel). 他住在里兹旅馆。 I stayed with my aunt when I was in London. 我在伦敦时，暂住在我姑妈家。 I'm not staying at a hotel,I'm staying with friends. 我没有住旅馆，我住在朋友家里。 Will you stay to (for) dinner? 请留下来吃饭好吗？ Where did you stay when you went to Paris? 你去巴黎时，住在哪儿？ 不及物动词 vi. 持续；耐久 last out; endure He doesn't seem able to stay to the end of the race. 看样子他不能撑到赛跑终点。 The shop stays open till eight o'clock. 商店开到八点。 及物动词 vt. （文学）抑制；止住；使停止 (lit.)check or stop the progress of He stayed the work and had the machinery removed. 他把工作停下来，将机器给移走了。 及物动词 vt. 暂时满足 satisfy for a little while Bill stayed his hunger by eating some crackers. 比尔吃些饼干充饥。

play 不同，是动词原形
stayed是stay 的过去式 ,cleaned是clean的过去式，都是规则变化