次數很少
這就是稀疏行事曆本身。
r · B2
Not often; only a few times over a long period, with long gaps in between.
不常、很少
核心畫面
Picture marks on a calendar that are spread , with long empty stretches between them: the word is about how something is spread across time, and not about whether it is good or bad.
可以想成一張行事曆上零星的幾個記號。記號之間隔著大片空白。這個字講的就是「在時間上有多稀疏」。它只回答次數，不評價好…更多收起
可以想成一張行事曆上零星的幾個記號。記號之間隔著大片空白。這個字講的就是「在時間上有多稀疏」。它只回答次數，不評價好壞。記住這張稀疏的行事曆，第二個用法也就好理解了：在整組 not infrequently 裡，前面那個 not 把這些空白劃掉，於是原本稀疏的記號翻成「其實排得挺密的」。From the word’s history
From infrequent + -ly, or equally from in- + frequently; either way the in- is the negative one, so the word starts from frequent and turns it over.
來源記了兩條都說得通的路：infrequent 加 -ly，或是 in- 直接加在 frequently 前面。不管走哪一條，那個 in- 都是否定的 in-。也就是說，這個字是從 frequent（常發生的）翻過來的，所以核心永遠是在講頻率。
Wiktionary entry for “infrequently”, etymology_text supplied in this packet (kaikki extract, source_ref kaikki:3f6f69a190036ae4:1321315786:6019)
Two branches
兩個否定相消
在前面再加一個 not，把稀疏的畫面整個翻過來，變成「其實蠻常的」。
r · C1
Fairly often. The two negatives cancel each other, so saying that something happens not infrequently means it happens quite a lot.
其實相當常見