a holiday taken by a newly married couple
"The newlyweds spent their first week of marriage on a romantic honeymoon in Italy."
the early (usually calm and harmonious) period of a relationship; business or political
"The new administration began its honeymoon, passing several key reforms while enjoying strong public support."
The period of time immediately following a marriage.
"After their wedding, they spent three weeks on a tropical island during their honeymoon."
In plain English: A honeymoon is the first trip that newly married couples take together to celebrate their wedding and spend time alone as a pair.
"They spent their first week on vacation in Hawaii enjoying their honeymoon together."
Usage: The term refers specifically to the vacation or idyllic phase enjoyed by newlyweds shortly after their wedding, though it can also describe any initial period of smooth cooperation between partners in business or politics. Avoid confusing this noun with the verb form when discussing general marital life rather than a specific trip or temporary state of harmony.
To have a honeymoon (a trip taken by a couple after wedding).
"After tying the knot, the newlyweds flew to Hawaii to enjoy their honeymoon."
In plain English: To go on a honeymoon is to take your first trip together as newlyweds right after getting married.
"They decided to honeymoon in Paris right after getting married."
The word "honeymoon" comes from an older phrase meaning honey + moon, originally describing the time after a wedding when affection was expected to wane like the phases of the moon. Over time, this evolved into its current sense referring specifically to that first month following marriage as being the sweetest period for newlyweds.