dec·i·mate / ˈdesəˌmāt/ • v. [tr.] (often be decimated) 1. kill, destroy, or remove a large percentage or part of. ∎  drastically reduce the strength or effectiveness of (something): plant viruses that can decimate yields.2. hist. kill one in every ten of (a group of soldiers or others) as a punishment for the whole group.DERIVATIVES: dec·i·ma·tion / ˌdesəˈmāshən/ n.dec·i·ma·tor / -ˌmātər/ n.ORIGIN: late Middle English: from Latin decimat- ‘taken as a tenth,’ from the verb decimare, from decimus ‘tenth.’ In Middle English the term decimation denoted the levying of a tithe, and later the tax imposed in England by Cromwell on the Royalists (1655). The verb decimate originally alluded to the Roman punishment of executing one man in ten of a mutinous legion.

decimate kill one in every ten of (a group of people) as a punishment for the whole group; kill, destroy, or remove a large proportion of. In Middle English the term decimation denoted the levying of a tithe, and later the tax imposed by Cromwell on the Royalists (1655). The verb decimate originally alluded to the Roman punishment of executing one man in ten of a mutinous legion.

Historically, the meaning of the word decimate is ‘kill one in every ten of (a group of people)’. This sense has been more or less totally superseded by the later, more general sense ‘kill or destroy (a large proportion of)’, as in the virus has decimated the population. Some traditionalists argue that this and other later senses are incorrect, but it is clear that this is now part of standard English.

decimate exact tithe from; put to death one in ten of a number. XVII. f. pp. stem of L. decimāre, f. decimus tenth; see prec. and -ATE 3.
So decimation exaction of tithe XV; destruction of one in ten. XVI. — late L.