They had a disagreement on this issue and couldn't reach a consensus.

disagreement 是由前缀 dis-（表示"否定、相反"）和名词 agreement（"同意、一致"）组成的复合名词。dis- 表示否定，agreement 表示"一致"，所以 disagreement 的字面意思是"不一致"，即"分歧、异议"。