Incorrect spelling, explanation: both learners and native users of English tend to believe that the word compare has the same spelling as the word pair, which gives the incorrect form compair and in the past form compaired. However, only the pronunciation of the two words is similar while the spelling is different. Thus, the only correct form is compare, which in the past tense becomes compared.

Correct spelling, explanation: this popular English verb comes from the Latin word comparare, which also used to mean to compare. The correct spelling of the base forms compare and as it ends in -e, when you want to form the past tense, you only add a -d letter, without introducing any changes to the word. Therefore, the correct spelling is compared.

Definition of compare:
1. verb (past form) – used when you want to find out whether the two things are similar or different, or when you want to state that two things seem to be equal.
They compared the two schools and then chose a better one.
He compared the two flats in many aspects but still couldn’t decide which one he liked more.

Collocations with compare:
The verb compared is usually followed by the prepositions to or with:
She compared the new dress to the one she bought last year.

Some common expressions with the word compared include:
compared notes, compared favorably:
That was so insane that we used to work in the same company that we compared notes for hours!
This flat certainly compared favorably with the one we used to live in.