But now there was a listlessness about her, not the listlessness of the cat Augustus but more that of the female in the picture in the Louvre, of whom Jeeves, on the occasion when he lugged me there to take a dekko at her, said that here was the head upon which all the ends of the world are come.
- PG Wodehouse, Jeeves in the Offing
A dekko/dekho/decko is a look. It was borrowed as army slang in the late 1800s from Hindi देखो dekho, the imperative of देखना dekhanā "to look". This is derived in some fashion from Sanskrit द्रक्ष्यति drakṣyati, the future of दृश् dr̥ś "to see". And dr̥ś is from Proto-Indo-European *derḱ- "to look".
I've written about this root before. It's thought that it gives us tarragon thru a convoluted series of borrowings - Greek δράκων "dragon" to Arabic طرخون ṭarẖwn then back to Greek as ταρχών, then Latin as tragonia/tarchon, then English tarragon. Tarragon is also known as dragonwort, and its Latin name is dracunculus.