Narodnaya Volya (The People's Will) was the organization responsible for the assassination of Tsar Alexander II in in March 1881. Is there any evidence (preferably online sources) which point to the idea that the organization was called "terrorist" by their contemporaries?
Yes, Alexander Ulyanov was one of the leaders of the terroristic fraction of the People's Will.
After the failed assassination of Alexander III, he pleaded guilty to conspiring to participate in a terrorist group. Ulyanov was also one of the authors of the terroristic fraction's program.
The court materials and the whole program was later published in the book by his sister: Ulyanova-Elizarova A. I. "Alexander Ulyanov and the case of 1 March 1887" (Ульянова-Елизарова А. И. Александр Ильич Ульянов и дело 1 марта 1887 г., partially available online).
From his testimony:
Я признаю свою виновность в том, что принадлежа к террористической фракции партии «Народной воли», принимал участие в замыслах лишить жизни Государя Императора.
I plead guilty that I, being a member of the terroristic fraction of "The People's Will", took part in the plans to take the life of the Sovereign Emperor.
From the Program (Ulyanov recorded this version of a program from his own memory while in prison):
... когда у интеллигенции была отнята возможность мирной борьбы за свои идеалы и закрыт доступ ко всякой форме оппозиционной деятельности, то она вынуждена была прибегнуть к форме борьбы, указанной правительством, т.е. к террору.
Террор есть, таким образом, столкновение правительства с интеллигенцией, у которой отнимается возможность мирного, культурного воздействия на общественную жизнь. ...
... when the intelligentsia was deprived of the possibility of a peaceful struggle for their ideals and access to any form of opposition activity was closed, it was forced to resort to the form of struggle indicated by the government, i.e. to terror.
Terror is, therefore, a clash between the intelligentsia and the government, which has taken away the possibility of a peaceful, cultured impact on public life. ...
So, at least some members of "The People's Will" self identified as terrorists and accepted terroristic acts as an appropriate means of political struggle.