tonicisation
The brief treatment of a non-tonic chord as a temporary tonic through the use of its own dominant or leading tone
In Depth
Tonicisation lasts only a chord or two — long enough to confirm a temporary tonic but too brief to establish a new key. It is achieved by introducing the temporary tonic's leading tone, typically through a secondary dominant (V/x) or secondary leading-tone chord (vii°/x). If the new tonal centre persists for a full phrase or longer with a cadence, it becomes a modulation rather than a tonicisation. The distinction is one of duration and structural weight.
The difference between tonicisation and modulation is one of the most-debated boundaries in music theory — experts disagree on exactly where one ends and the other begins.