1. case / situation
case = the actual state of affairs
There is a case for doing nothing at present.
The judge stated the case.
situation = set of circumstances
He has just come out of a very difficult situation
2. especially / specially
especially = particularly
I like the countryside, especially in spring.
specially = for a particular purpose
I came here specially to see you.
I made this cake specially for you.
3. realise / understand
realise = be aware of
I realised that I was wrong.
Haven't you realised that they don't want to see you again ?
(a) get the meaning of (character, language, difficulty)
Do you understand German ?
They're great friends and understand each other.
I quite understand your difficulty.
(b) take for granted
I understand that expenses were to be paid.
Am I to understand that you have resigned?
(c) grasp the significance or nature of something
I just can't understand why he didn't keep his promise.