There are many meanings of the prefix ‘para-’. Originally, in the Greek language, it meant “to one side of” or “beside”. The words ‘parabola’, ‘paragraph’, and ‘parallel’ all derive from this meaning.
When ‘para-’ is used in the title of an occupation, it means “like, but differing in some important respect”. A ‘paramedic’ is like a medical doctor, but has less advanced qualifications and lower status. A ‘paralegal’ is like a lawyer, but he/she, too, has less advanced qualifications and lower status.
In scientific terms, it often denotes “abnormal” or “defective”. ‘paranoia’ is an abnormal version of the processes that usually take place in a person’s mind.