Found:

functor

MORPHOLOGY: a notion which DiSciullo & Williams adopt from Categorial Grammar to express relationships between entities. EXAMPLE: if one wishes to express the idea that y is the sister of x, the property 'sister of' can be formalized by using a functor, say F, and write 'y=F(x)'. See Function composition.

LIT.	Di Sciullo, A. M. and E. Williams (1987)