transitive verb
Definition 1
Perceive, mark, watch, take notice of.
Source: Concise Oxford Dictionary
Context: We observed symptoms of pulmonary embolism in chest x-rays taken routinely in three patients.
Source: www.springerlink.com
Definition 2
Keep, follow, adhere to, perform duly (law, command, appointed time, method, principle, silence, rite, anniversary, etc.).
Source: Concise Oxford Dictionary
Context: The monks [in the film 'The Great Silence', about Carthusian monks in the French Alps] observe strict silence.
Source: forum.catholic.org