<P> The main discussion of these abbreviations in the context of drug prescriptions and other medical prescriptions is at List of abbreviations used in medical prescriptions . Some of these abbreviations are best not used, as marked and explained here . </P> <Table> <Tr> <Th> Abbrev . </Th> <Th> Meaning </Th> <Th> Latin (or New Latin) origin </Th> </Tr> <Tr> <Td> a.c. </Td> <Td> before meals </Td> <Td> ante cibum </Td> </Tr> <Tr> <Td> a.d., ad, AD </Td> <Td> right ear </Td> <Td> auris dextra </Td> </Tr> <Tr> <Td> a.m., am, AM </Td> <Td> morning </Td> <Td> ante meridiem </Td> </Tr> <Tr> <Td> nocte </Td> <Td> every night </Td> <Td> Omne Nocte </Td> </Tr> <Tr> <Td> a.s., as, AS </Td> <Td> left ear </Td> <Td> auris sinistra </Td> </Tr> <Tr> <Td> a.u., au, AU </Td> <Td> both ears together or each ear </Td> <Td> aures unitas or auris uterque </Td> </Tr> <Tr> <Td> b.d.s, bds, BDS </Td> <Td> 2 times a day </Td> <Td> bis die sumendum </Td> </Tr> <Tr> <Td> b.i.d., bid, bd </Td> <Td> twice a day / twice daily / 2 times daily </Td> <Td> bis in die </Td> </Tr> <Tr> <Td> gtt., gtt </Td> <Td> drop (s) </Td> <Td> gutta (e) </Td> </Tr> <Tr> <Td> h., h </Td> <Td> hour </Td> <Td> hora </Td> </Tr> <Tr> <Td> h.s., hs </Td> <Td> at bedtime or half strength </Td> <Td> hora somni </Td> </Tr> <Tr> <Td> ii </Td> <Td> two tablets </Td> <Td> duos doses </Td> </Tr> <Tr> <Td> iii </Td> <Td> three tablets </Td> <Td> trēs doses </Td> </Tr> <Tr> <Td> n.p.o., npo, NPO </Td> <Td> nothing by mouth / not by oral administration </Td> <Td> nil per os </Td> </Tr> <Tr> <Td> o.d., od, OD </Td> <Td> once a day right eye </Td> <Td> omne in die oculus dexter </Td> </Tr> <Tr> <Td> o.s., os, OS </Td> <Td> left eye </Td> <Td> oculus sinister </Td> </Tr> <Tr> <Td> o.u., ou, OU </Td> <Td> both eyes </Td> <Td> oculus uterque </Td> </Tr> <Tr> <Td> p.c. </Td> <Td> after food </Td> <Td> post cibum </Td> </Tr> <Tr> <Td> p.m., pm, PM </Td> <Td> afternoon or evening </Td> <Td> post meridiem </Td> </Tr> <Tr> <Td> p.o., po, PO </Td> <Td> orally / by mouth / oral administration </Td> <Td> per os / nonstandard form per orem </Td> </Tr> <Tr> <Td> p.r., pr, PR </Td> <Td> rectally </Td> <Td> per rectum </Td> </Tr> <Tr> <Td> p.r.n., prn, PRN </Td> <Td> as needed, (also Pertactin - a key antigen of ac. Pertussis vaccine) </Td> <Td> pro re nata </Td> </Tr> <Tr> <Td> q . </Td> <Td> every </Td> <Td> quaque </Td> </Tr> <Tr> <Td> q. 1. d., q1d </Td> <Td> every day </Td> <Td> quaque die </Td> </Tr> <Tr> <Td> q. 1. h., q1h </Td> <Td> every hour </Td> <Td> quaque hora </Td> </Tr> <Tr> <Td> q. 2. h., q2h </Td> <Td> every 2 hours </Td> <Td> quaque secunda hora </Td> </Tr> <Tr> <Td> q. 4. h., q4h </Td> <Td> every 4 hours </Td> <Td> quaque quarta hora </Td> </Tr> <Tr> <Td> q. 6. h., q6h </Td> <Td> every 6 hours </Td> <Td> quaque sexta hora </Td> </Tr> <Tr> <Td> q. 8. h., q8h </Td> <Td> every 8 hours </Td> <Td> quaque octava hora </Td> </Tr> <Tr> <Td> q.a.m., qAM, qam </Td> <Td> every morning </Td> <Td> quaque ante meridiem </Td> </Tr> <Tr> <Td> q.d., qd </Td> <Td> every day / daily </Td> <Td> quaque die </Td> </Tr> <Tr> <Td> q.h.s., qhs </Td> <Td> every night at bedtime </Td> <Td> quaque hora somni </Td> </Tr> <Tr> <Td> q.d.s, qds, QDS </Td> <Td> 4 times a day </Td> <Td> quater die sumendum </Td> </Tr> <Tr> <Td> q.i.d, qid </Td> <Td> 4 times a day </Td> <Td> quater in die </Td> </Tr> <Tr> <Td> q.h., qh </Td> <Td> every hour, hourly </Td> <Td> quaque hora </Td> </Tr> <Tr> <Td> q.o.d., qod </Td> <Td> every other day / alternate days </Td> <Td> quaque altera die </Td> </Tr> <Tr> <Td> q.p.m., qPM, qpm </Td> <Td> every afternoon or evening </Td> <Td> quaque post meridiem </Td> </Tr> <Tr> <Td> q.s., qs </Td> <Td> a sufficient quantity (enough) </Td> <Td> quantum sufficiat </Td> </Tr> <Tr> <Td> Rx, R,, ℞ </Td> <Td> prescription </Td> <Td> recipe </Td> </Tr> <Tr> <Td> Sig., S . </Td> <Td> directions </Td> <Td> signa </Td> </Tr> <Tr> <Td> Stat . </Td> <Td> immediately, with no delay, now </Td> <Td> statim </Td> </Tr> <Tr> <Td> t.d.s, tds, TDS </Td> <Td> 3 times a day </Td> <Td> ter die sumendum </Td> </Tr> <Tr> <Td> t.i.d., tid </Td> <Td> 3 times a day </Td> <Td> ter in die </Td> </Tr> <Tr> <Td> u.d., ud </Td> <Td> as directed </Td> <Td> ut dictum </Td> </Tr> </Table> <Tr> <Th> Abbrev . </Th> <Th> Meaning </Th> <Th> Latin (or New Latin) origin </Th> </Tr>

How do you write twice a day in medical terms