What is the appropriate term to describe the 6-month period between equinoxes, when the earth's axis is tilted towards the sun? Most dictionaries define summer as only the warmest months, June to August (in the Northern hemisphere).
Not that I am whole-heartedly suggesting this as a viable modern sense, but during elder days in the Northwest of our world, the word for the period extending from the vernal equinox to the autumnal one was quite simply Summer — nothing more, and nothing else.
There were only two seasons not four in this system, and we preserve this even today in our own Midsummer and Midwinter. That is why its midpoint at the solstice is called Midsummer’s Day. That is also why the midpoint of Winter is on Midwinter’s Day, which is the opposite solstice.
Alfta Lothurrsdottir discusses this in her Religious Practices of the Pre-Christian & Viking Age North under time-keeping:
Iceland, Greenland, and indeed also England reckoned the year into having two seasonal halves. That means that old records that measured things in seasons were actually twice as long than many casual readers would reckon things: eight seasons ago is four years, not two.
It is not hard to see why they did this. In Reykjavík during midsummer, the sun never completely deserts them, and during midwinter, it is hardly to be seen.
We can see this in our earliest records of the words in English, where winter and summer — or equally, summer and winter — was how one specified a full year. Citations from the OED:
Time was reckoned differently then. They would often count years by counting winters, and so a man of twenty winters was a twenty-year-old, just as a two- or three-year-old was a twinter and a thrinter respectively.
However, even their ideas of summer and winter were not quite ours. For them, the summery half the year began during mid-to-late April, and the wintry half during mid-to-late October. Samhain marked the end of the harvest and the beginning of winter, and Beltain, close to our own May Day, the beginning of summer. The cross-quarter days were useful in the common mindset, because of the thermal inertia that causes the apparent season to lag behind the actual solstices and equinoxes.
It wasn’t too long after the invasion of the southern occupiers from Normandy that the sense of a four-season year began to evolve:
That is, not just summer and winter, but also a lenten season and a harvesttide.
The period between equinoxes would be interequinoctial:
The term appears to be a little dated.