(twig) noun
A small shoot or branchlet of a tree. ♦ Collateral adjective: viminal. [OE twigge]
—twig′less adjective

(twig) v. twigged, twig·ging Slang v.t.
1. To observe closely; notice or watch.
2. To comprehend; understand.
—v.i.
3. To understand. [Cf. Irish tuigim I understand]

(twig) noun Archaic
The fashion: an old fop in good twig. [? <obs. twig act vigorously; ult. origin uncertain]