rhythm method 
noun
A method of avoiding conception favoured by the Roman Catholic Church, by which sexual intercourse is restricted to the times of a woman’s menstrual cycle when ovulation is least likely to occur.Popes Pius XI and XII went much further, allowing couples to take means to avoid procreation: the rhythm method or natural family planning....
- By now, I take it, the rhythm method of contraception must have passed out of favour.
- Many of Dr Jonas' female patients were Catholics, practising the rhythm method of contraception.
- notion store
- notitia
- not just any ——
- Notkerian
- not know from nothing
- not know if one is coming or going
- not know one is born
- not know one's arse from one's elbow
- not know shit
- not know shit from Shinola
- not know someone from a bar of soap
- not know someone from Adam
- not know that
- not know the first thing about
- not know the meaning of the word
- not know what hit one
- not know what to do with oneself
- not know where (or which way) to look
- not know where to put oneself
- not know which way (or where) to turn
- not least
- not let the grass grow under one's feet
- not-life
- not likely!
- not like the look (or sound) of