pretty/prettily

不同义。prettily 是形容词 pretty(漂亮的,美好的)的副词:

1. She was dressed prettily. (Palmer) 她穿得很漂亮。

2. She smiled prettily. (Collins) 她笑得很美。

而副词 pretty 在词义上与形容词并没有什么关系。它的意思是“相当”(rather, quite)或“很”(very):

1. I thought it was pretty good. (EED) 我认为那是相当好的。

2. It was a pretty poor imitation. (Dreiser) 那是一件很糟的仿制品。

3. She drives pretty fast. (CGEL) 她车开得很快。