one of these days—
1. (also: one of these fine days) at some time in the future that may be very soon (used as a promise or prophecy):
- One of these days he will find a farm to let, big enough to bring up little children on it.
2. said of a day that is full of mishaps; a day when everything seems to go wrong:
- I had the feeling as soon as the Johnsons trooped in for coffee that it was going to be one of these days.
Note:
a) The expression does not correlate in meaning with the phrase these days—nowadays; at present:
- These days candidates send swarms of advance men into every city before they arrive.
b) The expression does not correlate in meaning with the phrase one day—(also: one fine day)
1. at some distant time in the future:
- One day she will be married and we all will somehow have to live without her.
2. on a certain day in the past:
- He came to me quite unexpectedly one day and asked me to join his business.
one of those days— = one of these days 2:
- Oh, it’s one of those days. I bet you anything the horse breaks its legs.