adj

• (of a person) Deviating from the norm; behaving unexpectedly or differently; unconventional and slightly strange.
  "1801, Author not named, Fyfield (John), entry in Eccentric Biography; Or, Sketches of Remarkable Characters, Ancient and Modern, page 127, He was a man of a most eccentric turn of mind, and great singularity of conduct."
• (physiology, of a motion) Against or in the opposite direction of contraction of a muscle (such as results from flexion of the lower arm (bending of the elbow joint) by an external force while contracting the triceps and other elbow extensor muscles to control that movement; opening of the jaw while flexing the masseter).
• (mycology) Having or being an oospore with a single large oil globule on one side that displaces much of the ooplasm and forces the ooplasts to one side.
  "Oospores may be centric, subcentric, subeccentric or eccentric. Antheridial branches may or may not be present, and are androgynous, monoclinous, diclinous or hypogynous."

noun

• (slang) A kook; a person of bizarre habits or beliefs.
• (geometry, astronomy) A circle not having the same centre as another.
• (engineering) A disk or wheel with its axis off centre, giving a reciprocating motion.
  "The position of the eccentrics which is necessary to make the pistons drive the engine forward must be directly the reverse of that which would cause them to drive the engine backwards. To be able, therefore, to reverse the motion of the engine, it would only be necessary to be able to reverse the position of the eccentrics, which may be accomplished by either of two expedients."
• (physiology) An exercise that goes against or in the opposite direction of contraction of a muscle.
  "Research tells us that eccentrics, heavy partials, and static exercise may require several days or weeks of recovery time."