What is the origin of the expression "to twig to something"?

Question

Oddly enough, the OED (1971 Compact Edition) has no entry for twig to, only for twig something:

twig v⁴ slang or colloq. [Origin unascertained]

[...]

b. To become aware of by seeing; to perceive, discern, catch sight of; to recognize.

1796 J. G. Holman Abroad & at Home iii. ii, ― He twigs me. He knows Dicky here in his real and masquerade character both.

1801 M. G. Lewis Tales Wonder, Sailor’s T. ii, ― With strange surprise and fear, Jack Tackle’s ghost I twigg’d.

1825 Lady Granville Lett. 30 Jan. (1894) I. 339 ― They have twigged me.

1860 Hunting Grounds Old World Ser. i. xii. (ed. 2) 189 ― The leader, whom at last I twigged lying down and chewing the cud.

1879 F. Pollok Sport Brit. Burmah I. 191, ― I twigged the tigress creeping away in front of us.

Still, that's clearly the same as twig to so it will serve. What is the origin of this expression? Neither the OED nor etymonline.com provide any etymological information for this meaning of the word twig. It occurred to me that it might come from a hunting/tracking analogy where the sound of a broken twig would alert the hunter to the presence of their prey or the prey to the presence of the hunter. Is there anything to this or am I making it all up?

Answer 1

Wiktionary says this verb twig is from Irish and Scottish Gaelic tuig ‎(“to understand”).

Irish editor Stan Carey wrote on the Macmillan Dictionary blog in September 2014:

At an early age in Ireland I learned the Irish word tuig, meaning ‘understand’, often used in common phrases like An dtuigeann tú? (‘Do you understand?’). You can hear several regional pronunciations of the word at the excellent Irish dictionary website Foclóir.ie. Comparing tuig with twig we [World Wide Words writer Michael Quinion, and Carey] find they sound alike and mean similar things. Of course, this could simply be coincidental – but the correspondence, while inconclusive, is certainly suggestive.

Terence Dolan’s Dictionary of Hiberno-English says this Irish derivation for twig is possible, while Loreto Todd’s Green English says it ‘may well’ be the origin. Bernard Share’s Slanguage is less convinced, indicating instead that the two words have been confused. That’s a possibility, and it should be noted that tuig ‘understand’ is a word in Scottish Gaelic too. So the etymology of the verb twig remains uncertain, but Irish tuig seems to me a good candidate. If you’ve other ideas, let us know in the comments.

A comment from Colin McCarthy reads:

Your suggested derivation receives some support from Sean Beecher (1991 A Dictionary of Cork Slang The Collins Press). To quote from page 103, “Twig, To, verb. To understand. Use: You twig? You understand? Derivation: Possibly Irish ‘Tuig’ – to understand. And note ‘Twig’ – a divining rod for water, hence by extension ‘understanding’. Wright. And also ‘Twig’ – I catch your meaning, I understand (Irish ‘Tuigim’ – I notice). Brewer.”

And this comment from Michael Parsley:

Webster’s International Dictionary gives, in addition to the meaning of a ‘small shoot without leaves’, the meaning of to use a twig as a diving rod (searching for water).

This might be a source of the meaning to understand (suddenly).

Answer 2

In a phrase like 'Why don't you twig on to the fact that ....' that sounds very similar to the present tense of Irish tuig, which is tuigeann (pronounced closely to 'twig on'). In Irish,'she understands ...' would be 'tuigeann sí ...'.

Irish sí is pronounced extremely closely to English she and has the same meaning in this context.

The Irish tui has more of a glide sound than a full-on w, but an English ear could easily think there was a w in there.