Sometimes I am systematically working on things that require neo-Koine vocabulary, other times they arise somewhat spontaneously. The other day in class we were doing some Where are your Keys play and a student put their wristwatch on the table and said, τί ἐστι τοῦτο; as I have trained them to do. Of course, I had no word to hand for wristwatch and told them we would cover it next time.
The first thing I do when looking for a word is to consult two English->Greek lexica. The first is Woodhouse, found here, and the second is Edwards, found here. I search first for 'watch' but then for 'clock' as being more likely. Both suggest to use κλεψύδρα for clock. I then consult LSJ and find that it is a water-clock. Now, for some words once I consult LSJ I find that the choice is suitable. In this case, I feel like this is not quite adequate. And of course, some times Woodhouse and Edwards have nothing to offer.
If I find nothing at all, I check with Juan Coderich's list here.
Then, supposing I don't find anything useful in these steps, I retro-engineer. I consult an English-Modern Greek lexicon. Here's one I regularly use, Word Reference. Now I see that ρολόι is a common Modern Greek word for 'watch'. I go back to LSJ and other sources to try and determine the source of ρολόι. Sometimes it is easy to see where a word has derived from. In this case, it's not immediately obvious, so I do an etymological search, and discover that it comes from the Koine ὡρολόγιον. Now we have got somewhere. I can reconsult LSJ which has an entry for ὡρολόγιον under ὡρολογικός in the Supplement. it's a sundial or other device for telling the time. It's meaning is clear, and more adaptable than κλεψύδρα.
The last step here is to make it specifically 'wristwatch'. A simple genitive will do: τὸ ὡρολόγιον τῆς χειρός. voila. This is how we neo-Koinify the world.