second line
noun
1- anything used or held in reserve as support, replacement, or reinforcement, in particular（用作支援、替补或增援的）预备之物, 尤指：
1.1
- usu. as modifier a medical treatment or therapy used in support of another, or as a more drastic measure if the primary treatment is ineffective辅助治疗。
1.2
- a battle line behind the front line to support it and make good its losses第二战线。
1.3
- as modifier ranking second in strength, effectiveness, ability, or value二流的; 二等的：
the clutch of second-line US computer manufacturers.
一些美国二流计算机生产商。
1.4
- as modifier denoting shares that are not traded on the main stock exchange and are not subject to the same degree of regulation二线股。