The word has been in use in English since the 16th century. 'Honey' conveys a sense of sweetness and 'moon' suggests a period of one month. Put together, they mean that period immediately after a marriage during which the couple's relationship is at its sweetest and most tender. A more cynical suggestion is that it implies that - just as the moon is no sooner full than it starts to wane - so will the affections of the pair. Take your pick!
If you're really inspired to recreate a 14th or 15th century wedding reception, the drink of choice was Honeymead, a rich wine mixed with honey, cardamom, and cloves. The term "honeymoon" came from the month after the wedding when the bride and groom were supposed to drink this beverage every night to celebrate - the period of one moon - thus the after-wedding celebration we know today.
Mead [I'm guessing it must be the same thing] is also an aphrodisiac. [Depends on your palette - it's a bit sweet] but having been to a friends wedding recently the hotel gave out freebies [only minatures] of it. We were on a table of 20+ I was the only one who tried it [and liked it] we were given all the unopened ones - Oh lucky me, Mrs P is threatening to lock bedroom door!! heh heh!! Open fire, kids in bed; dog asleep, get snugged up with partner and a glass or 2 of it woof!