Practice, practise — English usage the noun is spelt with a ‘c’ and the verb with an ‘s’. In American usage practice is used for both noun and verb.
Precede, proceed — precede means to go before in place, order, rank or time;
There was some dispute over who should precede the archbishop in the ceremony.
Proceed means to go or move forward, specially after stopping;
After the interruption at the entrance the party was allowed to proceed.
Definite, definitive — these words are easily confused. Definite means clearly defined, precise or exact:
They were awaiting a definite reply to their question.
Definitive means conclusive or final:
Their offer is a definitive one and must be either accepted or rejected.
Delusion, illusion — a delusion is a mistaken belief that something really exists and cannot be removed by an appeal to reason:
She suffered from the delusion that all her food was poisoned.
An illusion is a false mental image which may result from a misinterpretation of something real or from something imagined:
He was under the illusion that he was really quite popular.
Amend, emend — Amend means to improve or make better:
He was told to amend his ways.
Emend means to remove errors or to correct and is used only in connection with manuscripts or printed matter:
They emended the document to the best of their ability.
Historic, historical — these words are frequently confused but their meanings are quite distinct. Historic means well-known or important in history.
Hastings was a historic battle.
Historical means connected with or relating to history:
A historical novel, historical evidence.
Lightening, lightning — lightening is the lessening of weight, while lightning is the flash of light in the sky caused by electrical charge.
Momentary, momentous — despite similar spellings these adjectives have very different meaning. Momentary means lasting only very briefly:
He caught a momentary glimpse of a very beautiful woman.
Momentous means of great importance or having far reaching consequences:
His decision was a momentous one for the future of the world.
Sceptic, septic — similarity is spelling can lead to confusion between these two words, although their meanings are entirely different. Sceptic is a noun and means one who maintains a doubting or distrustful attitude towards people, ideas, etc. Septic is an adjective meaning affected by a microbe or bacteria.
Elusive, illusory — the meaning of these two adjectives are sometimes confused. Elusive means hard to grasp, express or define, and has the alternative form illusory:
Her poetry had an elusive quality about it.
Illusory means of the nature of an illusion, deceptive or unreal:
His apparent success in his job was proved illusory when he was forced to resign.
Insolate, insulate — insolate is to expose to the sun’s rays, or treat by exposure to the sun.
Insulate is to cover or surround something, specially an electric wire, with non-conducting material.