Early 20th century; earliest use found in George Gould (1848–1922). From the initial letters of post-classical Latin quater in die four times a day or classical Latin quāque diē every day.
Definition of q.d. in US English:
q.d.
adjective
1Q.i.d. adverb (now disused).
2‘every day’.
Origin
Early 20th century; earliest use found in George Gould (1848–1922). From the initial letters of post-classical Latin quater in die four times a day or classical Latin quāque diē every day.