Dictionary:

overriding

  (ō'vər-rī'dĭng)

Also from Answers.com... ADHD Learn how to spot the signs.

First in priority; more important than all others: Our overriding concern is the eradication of illiteracy.

Definition: central, most important
Antonyms: insignificant, irrelevant, least, unimportant

1. First in priority; more important than all others.
2. Of or relating to a fracture in which the broken ends of the bone slip past each other and are held in the overlap position by contracted muscles.
3. Of or relating to a fetal head that is palpable above the pubic symphysis because of the disproportion between the size of the fetal head and the size of the maternal pelvis.

1. the position of fracture fragments in which they overlap one another.
2. anomalous positioning of major blood vessels, e.g. aorta or pulmonary arteries.
3. a law or order which overrides, or takes precedence over, a law or order of a court or legislature of lower standing.

• o. aorta — a congenital anomaly occurring in tetralogy of Fallot, in which the aorta is displaced to the right so that it appears to arise from both ventricles and straddles the ventricular septal defect.
• o. pulmonary artery — a congenital cardiac defect in which the pulmonary artery straddles a defective interventricular septum and the aorta originates in the right ventricle.

The adjective has one meaning:

Meaning #1: having superior power and influence
  Synonyms: paramount, predominant, predominate, preponderant, preponderating