Single-word replacement for "by definition"?

Software that is free is that which, by definition, has its full source code published.

I thought about definitionally, but after looking it up, it doesn't seem to be right.

Using defined as a verb provides a simple answer to the grammatical issue the question raises. However, the original statement and the suggested revisions of it are untrue. It is not the case that free software is defined as software whose full code is published. Although that is an intrinsic property of free software, it also is a property of freeware. In addition, some proprietary software is distributed as published source code, under restrictions like copyrights and non-disclosure agreements. Refer to wikipedia's article about Free Software for a better definition (eg, “Free software is computer software that is distributed along with its source code, and is released under terms that guarantee users the freedom to study, adapt/modify, and distribute the software”) and for further distinguishing characteristics.

To connect “Free Software” and “published source code” with by definition, is defined as, or definitionally is wrong. Instead say that having published code is an intrinsic, innate, or inherent property of Free Software.

Just use define as a verb.

Software which is free is defined as having its full source code published without encumbrance or fees.

• Free software, as such, necessarily has its full source code published.
• Software is free only if its full source code is published.