attacca

As a letter s

is the letter s with a.

As a verb attacca is

to tie.

In lang=en terms the difference between segue and attacca

is that segue is to make a smooth transition from one theme to another while attacca is without any break between the current movement and the next movement of the work.

As a verb segue

is to move smoothly from one state or subject to another.

As a noun segue

is an instance of segueing, a transition.

As an adverb attacca is

without any break between the current movement and the next movement of the work.