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Definition of Sub
Medically reviewed by Min Clinic Staff | Updated: January 2026
Sub-: Prefix meaning meaning under, below, less than normal, secondary, less than fully. As in subacute, subaortic stenosis, subarachnoid, subclavian, subclinical disease, subcutaneous, subdural, subglottis, subjacent, sublingual, subluxation, and subtotal hysterectomy. From the Latin preposition sub meaning under.
See also: Hypo-.