Even though the architecture is defined as both the structured description of a system and the structure of the system itself, the term "architecture" is mainly used, at least in the "electrical" industries, as the structured description of a system.
A note: architecture is often used in the construction industry to also denote an architectural style.
Typically, the design follows the architecture phase in a (new) system development process.
And while the architecture is rather "logical", the design is "physical", going down into the detail of the implementation technology.
In Zachman's, for instance, the system architecture model (logical) is followed down the column by the technology design model (system design some would say) (physical) (see http://www.mel.nist.gov/msid/SSP/standard_landscape/Zachman.html).
The architect describes a system (enterprise), in terms of components in interconnections etc, creating an architecture as such, in order to enable the usage, fixing and development of a system.
The designers take over the architecture, to completely specify the parts of the system architecture to the detail necessary for implementation, usage and development.
The architect can only specify a system to a degree. There cannot be an enterprise level designer (with rare exceptions) because nobody can ever understand all the parts of a complex system or an enterprise at the level of detail necessary to operate. Hence the system/solution designers, experts in different domains, take then over.
There can be only one enterprise level architect. But there are many designers, each specialised in a part of a system (architecture).