I almost literally bumped into this word recently. My local council has laid out a sundial in a patch of grass in front of the parish church. The accompanying panel explains that the sundial is of the analemmatic type. This word is in few of my dictionaries (and the panel’s author, naughtily, does not explain it), but it turns out to be a well-known technical term among those skilled in the mathematics needed to design sundials. It refers to a scale that shows the seasonal difference between time as shown by clocks and by the sun.
The more common sort of sundial has an angled post (usually called the gnomon, or sometimes the style) which casts a shadow on a circular dial. Its analemmatic cousin, on the other hand, has a vertical gnomon, which casts a shadow on an elliptical scale. For it to tell the time with adequate accuracy (you may recall Hilaire Belloc’s verse complaint: “I am a sundial, and I make a botch, of what is done much better by a watch”), the gnomon must first be moved to the correct position along a north-south axis according to the season. Though a small sundial of this type is rather fiddly to make and use, large ones laid out on a flat area permit a person to act as the gnomon (my local one is of this sort). Earnest enquirers after chronological intelligence then need only position themselves at the appropriate spot along the axis for the time of year and — weather permitting — they can then read off the time by noting where their shadow falls on the scale.
The word is the adjective derived from analemma. One sense of this is a scale shaped like a figure 8, giving the declination of the sun and the equation of time for each day of the year. This shows how clock time differs from that given by the sun (which varies a little season by season because the Earth’s orbit isn’t exactly circular). It derives from Latin analemma for the pedestal of a sundial (and hence the sundial itself), which comes from the Greek word for a prop or support.