*deik-

The core idea of this root was:

showing, telling

It’s a rather large family, but most of its members have some notion of talking or information at their core.
The biggest group are the ones around the Latin branch of dicere and dicare, which meant to speak and to proclaim.

• diction (“how you say something”)
• dictionary (“word book”)
• dictate (“say”)
• Benedict (“speak well”)
• indict (“put in words”)
• verdict (“true word”)
• addict (“speak for/toward”, like a fan)
• contradict (“counter speak”)
• dedicate (“to declare a separate part” originally for declaring that something belongs to the Gods)
• condition (“speak together, agree”)
• predicate (“declare openly”)
• vindicate (“speak with authority”)
• syndicate (“speak into union”)
• indicate (“declare in”)
• paradigm (“declare beyond”)

And there are many other relatives, some of which are a real surprise.
Here’s an (incomplete) list:

• judge (originally: “justice-speaker”)
• digit (originally “finger, used to show number”)
• token (“sign”)
• toe (“finger”)
• teach (“show and tell”)
• index (“point into, show”)