Sumar-auki

Meaning of Old Norse word "sumar-auki"

As defined by the Cleasby & Vigfusson Old Norse to English dictionary:

sumar-auki

a, m. ‘summer-eke,’ the intercalary week, an Icel. calendar-term; the ancient heathen year consisted of 364 days, or twelve months of thirty days each, plus four days, which were the auka-nætr or ‘eke-nights’ (see above); the remaining day and a fraction was gathered up into an intercalary week, called ‘Summer-eke’ or ‘Eke-week,’ which in ancient times was inserted every sixth or seventh year at the end of summer, which in such years was 191 days long; the ‘Summer-eke’ was introduced by Thorstein Surt (Thorstein the Wise) in the middle of the 10th century, see Íb. ch. 4, and is still observed in Icel.; now that the Gregorian style is in use in Icel. the intercalary week is inserted every fifth or sixth year; thus the year 1872 is marked as the ‘first year after sumarauki,’ (the years 1860, 1866, and 1871 being years ‘with sumarauki’); 1872 sem er ‘fyrsta ár eptir Sumarauka,’ Icel. Almanack, 1872; the years 1864 and 1870 were ‘fjórða ár eptir sumarauka;’ thus in 1871 the summer had twenty-seven weeks, the eke-week being the 21st to the 27th of October.

Possible runic inscription in Younger Futhark:ᛋᚢᛘᛅᚱ-ᛅᚢᚴᛁ
Younger Futhark runes were used from 8th to 12th centuries in Scandinavia and their overseas settlements