cotton on to

• cotton onto

cotton on to (third-person singular simple present cottons on to, present participle cottoning on to, simple past and past participle cottoned on to)

1. (slang) To come to know or understand (something).
   • 2019 March 13, Drachinifel, 26:59 from the start, in The Russian 2nd Pacific Squadron - Voyage of the Damned‎, archived from the original on 29 January 2023:

     Buuut the Kamchatka eventually showed up, with news: whilst the main fleet had almost triggered a war with the British Empire, she'd managed to outdo them all, by reporting that, not only had she fired three hundred shells in an engagement with three Japanese ships, but, in fact, had shot at a Swedish merchantman, a German trawler, and a French schooner, putting the Russians at odds with almost every other major European fleet in existence. Fortunately, everyone else seemed to cotton on to the truly-appalling level of captaincy on the Kamchatka, and those incidents were quietly dropped. This was coupled with the fact that Kamchatka's truly-appalling levels of gunnery prevented it from having started several new wars, by not actually hitting anything.

2. (slang, archaic) Synonym of cotton to (“like, tolerate”)

• John Camden Hotten (1873) The Slang Dictionary