不等于任何单词
used to do sth，是典型的动词过去式形式。因此它的否定形式和疑问形式，就如同任何其他过去式的动词⼀样要加助动词 did + use to...恢复原形。
1、use可以作动词和名词
(1) 作动词时，“使⽤，利⽤，服⽤（毒品）”
过去式used，过去分词used，现在分词using.
(2) 作名词时，“使⽤，使⽤权，功能”
形容词useful ， 副词usefully
2、关于use 的三个固定句型：
(1) used to do sth. "过去常常做某事"
(2) be used to do sth. "被⽤来做某事"
(3) be used to doing sth "习惯做某事"
3、辨析：
(1)used to do sth. "过去常常做某事"
to 后加动词原形，否定句为didn't use to或used not to
如: I used to take a walk after supper every night.
(我过去常常在每天晚上饭后去散步)
(2) be used to do sth. "被⽤来做某事"
to 后加动词原形
如: Wood is used to make paper.
(⽊材被⽤来造纸)
(3) be used to doing sth "习惯做某事"
to是介词，后加名词，动名词或代词
如: He is used to getting up early
