HyperDic: as_needed

English > 1 sense of the expression *as needed*:
ADVERB	all	as needed, as required, pro re nata, PRN	according to need (physicians use PRN in writing prescriptions)

English > *as needed*: 1 sense > adverb 1
Meaning	According to need (physicians use PRN in writing prescriptions).
Example	"add water as needed"
Synonyms	as required, pro re nata, PRN