t.d.s. means ter die sumendum - three times a day in Prescription
Similar to t.d.s.
a.u. - auris utraque - both ears aa - ana - of each ad - ad - up to ad lib. - ad libitum - use as much as one desires; freely admov. - admove - apply agit - agita - stir/shake alt. h. - alternis horis - every other hour