Generically an accountant or accounts clerk whose job concerns the fixing of monies due for work done in manufacturing a product (i.e. reckoning the cost of material and labour consumed) but who is increasingly called upon to estimate the probable unit cost of a manufacturing process so that a price can be projected for the purpose of making a tender. In this sense the work is closely allied to that of a quantity surveyor.
In present usage the term cost accountant has taken on a far wider meaning. Cost and management accounting concern the everyday running of a business, as opposed to financial accounting, which deals with the problems of obtaining and accounting for the necessary finance. Cost accountants are also closely connected with budgeting and budgetary control. It is the cost accountant who is responsible for obtaining many of the figures on which a budgetary control system is based.
Reference: The Penguin Business Dictionary, 3rd edt.