In astrology, a semi-square is an astrological aspect that two planets make when they are 45° apart from each other. The semi-square is considered to be the 8th harmonic of the chart because it is one-eighth of the 360° circle that the zodiac resides in (i.e., 360 / 8 = 45). The semi-square is considered to be a minor hard aspect because it is thought to cause friction in the native's life and prompt them to take some action to reduce that friction.
For example, if the Sun is posited in 10° Aquarius and Venus is posited in 25° Pisces then a semi-square would occur. This is thought to indicate that the native is not likely to be totally happy in matters of love. The native is thought to have a tendency to seek out those individuals who are not necessarily compatible to them, and this may lead to a sense of tension and actions to correct what to them may be frustration.