3 left-side heart (心) radical adjectives in Japanese that end in しい
The title is pretty self-explanatory. I find myself getting 怪しい ayashii, 惜しい oshii and 悔しい kuyashii mixed up on Anki sometimes, so this is more a note to self, but I hope others may also find this useful. I'll first reproduce (with some minor typographic edits and omissions for brevity) the dictionary entries given in the Sankoku dictionary (三省堂国語辞典 4th ed.)
怪しい・あやしい： 1）ようすがおかしい。異様だ。 2）うたがわしい。信用できない。 3）男女の間で秘密の関係がありそうだ。
惜しい・おしい： 1）（人やものを）失うことが、残念だ。（例：時間が惜しい・惜しい人を失った） 2）そのもののねうちが現れなくて、残念だ。 3）手に入れることができなくて、残念だ。 4）（その状態が続けられなくて）残念に思う状態だ。（例：名残が惜しい。）
悔しい・口惜しい（！）・くやしい： 1）人に負けたり、恥ずかしい思いをさせられたりして、腹が立つような、泣きたいような感じだ。（もう、取り返しのつかないときに使う）
Of these 3 entries, I was most surprised by kuyashii, since a) it doesn't have a straightforward synonym (let's say, ayashii is roughly okashii and oshii is roughly zannen), but also b) the definition provided by Jisho.org for kuyashii is "vexing; annoying; frustrating; regrettable; mortifying", which I think doesn't capture the nuance as elicited from a Japanese dictionary (mortifying seems the closest, but mortifying comes off a little strong to my ear). I'd translate the Sankoku entry as: "That feeling when you are defeated or embarrassed by someone, and you feel angry and want to cry in [because of?] the helplessness of the situation."
As a memory aid, some other words and compounds that feature the kanji in these adjectives:
怪：怪獣 kaijuu 'monster', 怪我 kega 'injury', 妖怪 youkai 'yokai', 怪しむ ayashimu 'to [consider] suspect'
惜：惜しむ oshimu 'to consider [something] regrettable; to consider [unnecessary usage of something] a waste, i.e. to be frugal; to cherish; [also in the negative i.e. 惜しまない] (lit.?) 'to not skimp out on; do a lot of'. See extra note at end.
悔：後悔 koukai 'regret', 悔やむ kuyamu 'to regret; to mourn [someone's death].'
-----
NB: the on-yomi for 惜 is seki cf. Cantonese sek3, but Sino-Japanese compounds with 惜 seem quite uncommon, i.e. 痛惜 tsuuseki 'deep regret' 惜敗 sekihai 'regrettable defeat, defeat by a narrow margin'. Also in looking up sekihai, I found this concept which is delightfully nerdy.