首先

1.in the first place

2.first

Relative explainations:

3.begin...with

4.for one thing...(for another)

5.first of all

6.to begin with

7.imprimis

8.in the first instance

9.firstly

10.of all things

11.above all

12.to start with

13.primarily

14.threshold

15.at a first brush

16.first and foremost

17.the first thing

18.in the beginning