Hi Cheang,

c> I wonder if anyone can suggest how abhisallekhikaa should be
c> analysed.

There is an article in PED:

abhisallekhika (adj.) [abhi+sallekha+ika] austere, stern, only in f.
-aa (scil. kathaa) A III.117 sq.; IV.352, 357; V.67.

-ka is a usual ending of adjectives derived from nouns.

Metta,
Dimitry