What is the meaning of the abbreviations often used by a doctor when writing a prescription?

Latin Phrase	Shortened Form	Meaning
quaque hora	qh	every hour
quaque die	qd	every day
bis in die	bid	twice a day
ter in die	tid	three times a day
quarter in die	qid	four times a day
pro re nata	prn	as needed
ante cibum	a.c.	before meals
post cibum	p.c.	after meals
per os	p.o.	by mouth
nihil per os	n.p.o.	nothing by mouth
signetur	sig	let it be labeled
statim	stat	immediately
ad libitum	ad lib	at pleasure
hora somni	h.s.	at bedtime
cum	c	with
sine	s	without
guttae	gtt	drops
semis	ss	a half
et	et	and