Doubt and suspect

To doubt is to think that something is unlikely.

I doubt if he will come.
I doubt whether you can finish the work in time.

To suspect is to believe that somebody is guilty or something is true.

How could they suspect him of murder?
I suspect that my servant has stolen my watch.

Drown and sink

Drown means ‘die by immersion in water’. In British English, both active and passive forms of drown can be used to talk about accidental drowning.

He drowned while swimming across the river. OR He was drowned while swimming across the river.

In American English, only active forms are used to talk about accidental drowning.

To sink is to go beneath the surface of water.

The explosion sank the ship. (NOT The explosion drowned the ship.)

Facility and felicity

Facility means something with a particular function.

A wide range of facilities is available at the sports center.

Felicity means intense happiness.

Only the virtuous can experience true felicity.

Hard and hardly

Hard means difficult.
You have given me a very hard problem to solve.

Hardly means scarcely
She had hardly arrived when she was put to work.

Prescribe and proscribe

To prescribe is to recommend remedy
Doctors should be wary of prescribing antibiotics for minor infections.

To proscribe is to ban something.