Full Idea
One simply would not know what it is to understand the meaning of a linguistic expression if one did not know how one could make use of it in order to reach understanding with someone about something.
Gist of Idea
To understand language is to know how to use it to reach shared understandings
Source
Jürgen Habermas (On the Pragmatics of Communications [1998], p.228), quoted by James Gordon Finlayson - Habermas Ch.3:34
Book Reference
Finlayson,James G.: 'Habermas' [OUP 2005], p.34
A Reaction
Not offered as a 'theory of meaning', and certainly plausible. Compare a hammer, though: a proper understanding is that it is used to exert a sharp force, but you can take in its structure and nature before you spot its usage.