Yes, rub is playable
...and is worth 7 points.
Found in the following dictionaries
Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
"Rub" Definition
noun
A seasoning made of ground spices and herbs, applied to the surface of meat, fish, or vegetables before cooking.
A substance or preparation applied by rubbing, especially:.
An act or remark that annoys or hurts another.
An unevenness on a surface.
verb-transitive
To apply pressure and friction to (a surface).
To apply to a surface firmly and with friction: rub lotion on the hands; rub dye into the fabric.
To cause to become worn, chafed, or irritated.
To clean, polish, or manipulate by the application of pressure and friction.
To move (an object or objects) firmly along a surface, especially repeatedly: rub an eraser over the blackboard; rubbed my fingers over the sore spot.
verb-intransitive
To be transferred or removed by contact or proximity: newsprint that rubbed off on my fingers; wished some of her luck would rub off on me.
To cause irritation or annoyance.
To exert pressure or friction on something.
To move along in contact with a surface; graze or scrape.
To wear or chafe with friction: My shoes were beginning to rub.
verb
To move along the surface of a body with pressure .
To fret or chafe with or as if with friction.
To cause discontent, irritation, or anger.
To continue in a situation usually with slight difficulty .
To admit of being rubbed (as for erasure or obliteration).
idiom
Elbows To mix or socialize closely: diplomats rubbing elbows with heads of state.
Rub (someone) the wrong way To annoy; irritate: "One can see . . . how [his] expression of his ideals and intentions must have rubbed many people the wrong way” ( Christopher Lehmann-Haupt).