| Definition - The situation where two linguistic elements can occur in the same environment, and replacing one with the other creates a difference in meaning.
For example, sounds are being used contrastively if switching one pronunciation for another could result in a change in meaning (pat vs. bat)
1. Two elements that contrast in identical environments make a minimal pair.
Example Usages -
1. "One of the most basic concerns of phonology is determining what phonemes constitute the phonological inventory of a given language, i.e. which sounds are used contrastively."
(Source: Ryan's linguistics blog )