The definition for colossal is "Immense, enormous." Used in a sentence: After pushing with all his might, Frank realized he could never move the colossal boulder.

The definition for commemorate is "To mark by a ceremony." Used in a sentence: Each year, the Franklins commemorate their anniversary by visiting the site of their first date.

The definition for periodic is "Occurring at regular intervals." Used in a sentence: The periodic innterruptions of the cuckoo clock prevented Li from concentrating.

The definition for placebo is "An inactive substance used in medical testing." Used in a sentence: Tom, who had taken the placebo, found that his allergy symptoms did not go away.

The definition for sociable is "Inclined to seek companionship." Used in a sentence: The sociable Glenda was delighted to receive the party invitation.