英语的对称词是什么意思?

day by day 逐日day after day 每日one by one 逐个bit by bit 一点点地little by little 渐渐地step by step 逐步地by and by 逐渐side by side 并排face (nose) to face (nose) 面对面back to back 背靠背hand in hand 手拉手arm in arm 挽手mouth to mouth嘴对嘴heart to heart 交心,谈心neck and neck 并驾齐驱eye to eye 赞同head to head 交头接耳shoulder to shoulder 并肩on and on 继续word for word 逐词地out and out 十足的inch by inch 一点一点地like for like 以牙还牙like attracts like 物以类聚wheels within wheels 复杂的结构diamond cut diamond 棋逢对手这些都是对称词