“Is” and “are” are linking verbs for the present tense of “to be.” English uses “is” for singular nouns and “are” for plural nouns.
The words port and starboard are nautical terms that describe the right and left sides of a water vessel.
Incase is not the same as the phrase "in case." Incase is a spelling variant of the verb encase and means ‘to enclose’ or ‘cover.’
The words ageing and aging are alternate spellings of the same word, but “ageing” is more common outside of the United States and Canada.
Gage and gauge often share the same meaning, but “gauge” is the preferred English spelling for topics regarding measurement, estimation, or mathematics.
The two words ‘compliment’ and ‘complement’ can often be confusing for those not sure of their differences.
The two words ‘defence’ and ‘defense’ can often be confusing for those not sure of their differences.
“Has” and “have” appear together for the present and perfect tenses of the verb “to have.”