Control account or Chart of account or control point are the terms related to WBS.

But cost of account is vague term ( or wrongly introduced term by mistake by some one (author)), and it is not relevant to WBS or synonym of Control Account.

In the tree structure ( work break down structure)  of project ( project statement of work)  to work package - control account can be defined as below:

Project ---- sub projects -------- phases -- deliverables ---- work packages  ----> control points -- identified as control account number-------- work packege (see PMBOK 4  p 118 and fig 5-8/ also glossary p430 - Control Account)

 Control Acccount , in between this break down structure is a point , which has one or many work packages for the purpose of management control.( see 5.3.3.1)

like this OBS (organization break down structure ) is also decomposed and termed as type of WBS  and may have control point/ control account.

So it can be said intersection of WBS or Organization chart is known as Control Account. 

but Cost account is different term ( of commerce and banking- related to cost amount and estimating)