A provisional trust and confidence. Translators sometimes use the word "faith" or "conviction", but those two words are problematic.
Ven. Bhikkhu Bodhi wrote: As a factor of the Buddhist path, (saddhā) does not mean blind belief but a willingness to accept on trust certain propositions that we cannot, at our present stage of development, personally verify for ourselves. These propositions concern both the nature of reality and the higher reaches of the path. In the traditional map of the Buddhist training, (saddhā) is placed at the beginning, as the prerequisite for the later stages comprised in the triad of virtue, concentration, and wisdom. http://www.accesstoinsight.org/lib/auth ... say_45.pdf
I haven't yet done an exhaustive search (looking at every single occurence of hiri and ottappa in the suttas), but I have looked at enough passages now to establish an STED (standard EBT definition) that occurs in several key passages.
It looks like the strongest tie in with the 4nt, 8aam, 37bp, etc, would be under right effort and viriya, where hiri and ottappa have a strong explicit connection with the STED right effort formula of "papaka akusala dhamma" (evil unskillful Dharma[teachings & qualities]), and also the sutta where ottappa and ātāpi are shown working together (they both have tapa, austerity, strong heat of effort in that word), and we know atapi is a key word in the 4sp (satipatthana) formula that references right effort.
Also several suttas, especially AN 4.169, have modified forms of 5bal and 5ind (bala and indriya) to incorporate hiri & ottappa. So those seem like the strongest explicit EBT tie ins that I can find so far.
But I am keeping a comprehensive encyclopedia entry for hiri & ottappa in the link above, so please feel free to share sutta references (with sutta ref number in modern numbering system, no PTS page number) on this thread and I'll add to collection. Thanks to all who contributed.