n, often attrib  1  :  a natural cover or top: as  a  :  PILEUS  b  :  PATELLA, KNEECAP  2  :  something that serves as a cover or protection esp. for a tip, knob, or end (as of a tooth)  3  Brit  :  CERVICAL CAP  4  :  a cluster of molecules or chemical groups bound to one end or a region of a cell, virus, or molecule <the cell surface receptors were redistributed into s> 
vb, capped  cap*ping vt  1  :  to invest (a student nurse) with a cap as an indication of completion of a probationary period of study  2  :  to cover (a diseased or exposed part of a tooth) with a protective substance  3  :  to form a chemical cap on <the capped end of a messenger RNA>  vi  :  to form or produce a chemical cap <erythrocytes and fibroblasts usually do not >  .
 
 
 
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