Waiting in the wings 
Ready to take an action

Walk in a park 
Smooth an easy

Walk on a green mile 
Going to do something which cannot be avoid

Walk on eggshells 
About to get very angry with someone

Walking on air 
Very happy

War of words 
A big argument

Waste of skin
Worthless

Watch the step 
Move / Act carefully

Watch the tongue
Speak carefully

Watching paint dry
Boring / not interesting at all

Wear many hats
People who play many roles or in many positions at the same time.

Wet behind the ears
Naive / no experience

White feather
The sign that the person is scared or highly nervous.

White knight
Person who like to help or save the others

White lie
Lie for a good purpose to help something/ someone.

Whole food
Organic food

Wide of the mark
Incorrect / Inaccurate

Wild card
Unpredictable factors

Window shopping
Go to the shop to walk and look around but not buying.

Wishy washy
Something unclear

With eyes open
Fully aware when doing something

Within a stone throw
Withing a very short distance

Word by word
Very word