1. [adj]  used especially of drugs or muscles that work together so the total effect is greater than the sum of the two (or more)
2. [adj]  capable of acting on or influencing each other

INTERACTIVE is a 11 letter word that starts with I.

1. A network simulation language.

   ["Design and Implementation of a Pascal Based Interactive Network Simulation Language", R. Lakshmanan, PhD Thesis, Oakland U, Rochester MI 1983].

2. A term describing a program whose input and output are interleaved, like a conversation, allowing the user's input to depend on earlier output from the same run.

   The interaction with the user is usually conducted through either a text-based interface or a graphical user interface. Other kinds of interface, e.g. using speech recognition and/or speech synthesis, are also possible.

   This is in contrast to batch processing where all the input is prepared before the program runs and so cannot depend on the program's output.