Websters:

1ad hoc
Pronunciation:(*)ad*h*k, -*k also (*)*d-
Function:adverb
Etymology:New Latin, literally, for this

: for the particular end or purpose at hand and without reference to wider application or employment *a special member appointed ad hoc according to the problem being considered

María Moliner
ad hoc.
Expresión latina de uso frecuente en lenguaje culto, que significa «a propósito»: no hecho ya o aplicable a cualquier caso, sino hecho precisamente para el caso de que se trata.
(V. «*adecuado, facticio».)