The defining conformity to context ordinarily concerns a complete communicative utterance, with its intended sense and chosen manner of expression. An isolated lexical item, not yet employed in such an utterance, does not by itself display that full conformity.
The word “knowledge” is meaningful. But whether to state “Knowledge is beneficial,” to add an example, or to supply evidence depends on a particular question and audience.
Thus the assessment of a fasih individual word must be distinguished from the balagha of complete discourse.