• Potential: possible when the necessary conditions exist:

A number of potential buyers have expressed interest in the company.
Many potential customers are waiting for a fall in prices before buying.
The accident is a grim reminder of the potential dangers involved in North Sea oil production.

More examples

Of course we don’t want to alarm people unnecessarily, but they should be alerted to potential dangers.
They went into the restaurant and handed out leaflets to potential customers.
We estimate the potential market for the new phones to be around one million people in this country alone.
We shall pilot several new cosmetic products to selected potential purchasers.
The potential benefits outweigh the problems.

• viable: able to work as intended or able to succeed:

In order to make the company viable, it will unfortunately be necessary to reduce staffing levels.
I am afraid your plan is not commercially/economically/financially/politically viable.

achievable = Make sure your weight-loss goals are achievable.
attainable = Employees benefit from having attainable goals.
doable = It’s a big ask, but it’s doable.
feasible = Given the lack of funding, is this plan really feasible?

• substitute: to use something or someone instead of another thing or person:

You can substitute oil for butter in this recipe.
Dayton was substituted for Williams in the second half of the game.

• fierce: physically violent and frightening:

a fierce attack/battle
Two men were shot during fierce fighting last weekend.

violent = Her ex-boyfriend was violent.
aggressive = She was very aggressive towards the TV reporters.
ferocious = A ferocious dog guarded the house.
fierce = The battle for the stronghold was fierce, with hundreds of soldiers killed.
savage = It was a savage attack.
brutal = He was jailed for the brutal crime.

• Flatter: to praise someone in order to make them feel attractive or important, sometimes in a way that is not sincere:

I knew he was only flattering me because he wanted to borrow some money.

praise = Lawmakers praised the bipartisan deal.
congratulate = I congratulated him on passing his driving test.
compliment = I was just complimenting Robert on the wonderful meal he has cooked.
commend = The judge commended her for her bravery.
pay tribute to = He paid tribute to the firefighters who had saved his daughter’s life.
flatter = I knew he was only flattering me because he wanted to borrow some money.

Speaking:

Are you a student?
What subjects are you studying?
Why did you choose these subjects?
Do you like your subjects? Why?
Are they interesting?
Do you prefer to study in the morning or evening?
Which is your favorite subject and why?
Which subject you find challenging?
Do you prefer to study alone or in groups?
How do you concentrate on your studies?

Speak on this topic for 2 minutes:

Describe a time when you had to wait in a long line