Is there a specific aviation term for suicide by pilot?
According to the German Wiki article about CFIT a pilot's suicide is indeed not a CFIT. It is instead denoted as SEC.
They refer to the document CAST/ICAO Common Taxonomy Team: Aviation Occurence CategoriesPDF (Rev. 4.7, page 21)
which says

SECURITY RELATED (SEC)
Criminal/Security acts which result in accidents or incidents (per Annex 13 to the Convention on International Civil Aviation).
Usage Notes:

While security-related acts can lead to accidents as defined as by Annex 13 to the Convention on International Civil Aviation, they are not considered accidents by some organizations. Regardless, these events have similar consequences in that they result in serious injury or death to person(s) and/or substantial damage to the aircraft. For these reasons, they are categorized as security-related occurrences for prevention purposes only.

Examples include, (a) hijacking and/or aircraft theft, (b) interference with a crewmember (e.g., unruly passengers), (c) flight control interference, (d) ramp/runway/taxiway security, (e) sabotage, (f) suicide, and (g) acts of war.



Also, (same document, page 9) about CFIT:

Usage Notes:
[…]

Do not use this category for occurrences involving intentional flight into/toward terrain in manned aircraft or intentional ground impact of unmanned aircraft. […] Code all suicides under Security Related (SEC) events.

[…]

(Emphasis mine)
So according to ICAO, all suicides are SEC but not all SEC are suicides.