Quoting John Ayto describing 'Honeymoon': "his description (Richard Huloet 1552) suggests not only that the term had already been around for some time by the 1550's but also that it was probably inspired by the notion that although married love was as sweet as honey, it soon waned like the moon."
Oxford English Dictionary
HONEYMOON noun: 1) ‘The first month after marriage, when there is nothing but tenderness and pleasure’ (Johnson); originally having no reference to the period of a month, but comparing the mutual affection of newly-married persons to the changing moon which is no sooner full than it begins to wane; now, usually, the holiday spent together by a newly-married couple, before settling down at home. 2) figurative use: The first warmth of newly established friendly relations.
Michael Quinion’s World Wide Words<1546 “It was yet but HONY MOONE.”— ‘Proverbs’ (1867) by John Heywood, page 14>
<1552 “HONY MONE, a terme prouerbially applied to such as be newe maried, whiche wyll not fall out at the fyrste, but thone loueth the other at the beginnynge excedyngly, the likelyhode of theyr exceadynge loue appearing to aswage, ye which time the vulgar people cal the HONY MONE, ‘Aphrodisia, feriæ, hymenæ.’”— ‘Abcedarium Anglico Latinum’ by Huloet>
<1580 “It being now but HONNIE MOONE, I endeauoured to courte it with a grace.”—‘Euphues and His England,’ page 289> [first figurative use]
<1612 “And now their HONEY-MOON, that late was clear, Doth pale, obscure, and tenebrous appear.”—‘Cornucopia’ by Breton>
<1867 “The brief HONEYMOON of the new king and his parliament.”—‘Three English. Statesmen (Pym, Cromwell, Pitt)’ (1882) by Goldwin Smith, page 7>
HONEYMOON: Those of you with romantic constitutions had better look away now. There are many invented stories about the origin of this word, mostly so sickly that I cringe at repeating them. There is, for example, the suggestion that at some time in some place there was a custom for newlyweds to drink a potion containing honey every day for the first month after the nuptials. But the word only turns up in English in the middle of the sixteenth century. Let me quote you a passage from Richard Huloet’s Abecedarium Anglico Latinumof 1552 (in modernised spelling): “Honeymoon, a term proverbially applied to such as be new married, which will not fall out at the first, but the one loveth the other at the beginning exceedingly, the likelihood of their exceeding love appearing to assuage, the which time the vulgar people call the honey moon”. Putting it simply, it was that charmed period when married love was at first as sweet as honey, but which waned like the moon and in roughly the same period of time. Cynical, I know, but that’s etymology!