-ar

(Latin: a suffix; pertaining to, of the nature of, like; denoting an agent)

ocellar
Referring to an ocellus.
ocular
1. In a microscope, the lens closest to the eye is termed the ocular (the eyepiece) whereas the objective lens is the lens nearest to the object being examined.
2. The light microscope today is usually binocular (with one ocular for each eye) and has a turret bearing a selection of objective lens.
3. Relating to, perceived by, or performed by the eye.
oracular
1. Of, relating to, or being an oracle.
2. Resembling or characteristic of an oracle; such as, solemnly prophetic, enigmatic, or obscure.
3. Holding or claiming the authority of an oracle; such as, he holds forth in an oracular fashion.
orbicular, orbicularis
Circular; spherical.
osmolar
Of or pertaining to the osmotic property of a solution containing one or more molecular or ionic species, quantitatively expressed in osmol units.
peregrinar
1. To travel from place to place, or from one country to another; especially, to go on foot in foreign countries.
2. To travel through a specific place.
periareolar
Around the pigmented tissue of the breast.
peribulbar
1. Surrounding the eye.
2. Pertaining to the tissues immediately surrounding the eye.
plantar (s) (noun), plantars (pl)
The bottom part of the feet: The new shoes were very comfortable for Linda's plantars.
pleiobar
1. An area of high barometirc pressure.
2. An isobar of high pressure.
plumalar
A reference to a plumula.
polar
polar opposites
popular
1. Regarded with favor, approval, or affection by people in general.
2. Treated with favor, approval, or affection by an acquaintance or acquaintances: "He's my most popular friend."
3. Representing the people; especially, the common people: "There is popular agreement against going war."
4. Of the people as a whole; especially, of all citizens of a nation or state qualified to participate in an election: popular suffrage; the popular vote; popular representation.
5. Prevailing among the people generally: "There is a popular trend for laptop computers."
6. Suited to or intended for the general masses of people.
7. Adapted to ordinary intelligence or taste; such as, popular articles on science.
8. Suited to the means of ordinary people; not expensive: "Popular prices on all tickets to the movie were offered."
rectilinear (adjective), more rectilinear, most rectilinear
1. Characterized by straight lines: Since Edward and his wife didn’t like flowery patterns for their wallpaper, they chose colorful one-dimensional, or rectilinear, patterns instead.
2. Etymology: "a straightforward line of descent", from Late Latin rectilineus which comes from the Latin words rectus, "straight" + linea, "line".

A lesser-known variant, "rectilineal", comes from the same Late Latin rectilineus and employs the -al suffix instead of -ar.

Rectilineal still shows up occasionally, but rectilinear is used much more.