A very appropriate yojijukugo for the sixty-ninth entry in the series. I can hardly believe it’s been over a year already!
Literally: thought – flavor – deep – long
Alternately: Containing deep meaning. Possibly this meaning is hidden, or suggestive, or simply profound; in any case it must be more than what’s going on on the surface of things.
Notes: 意味 (imi) is “meaning.”
Apparently some people replace 長 with 重 (“heavy”) or 深長 with 慎重 (“careful”). But while this doesn’t change the pronunciation, and none of my sources specifically condemn them, I would not recommend using these variants.