Sometimes one is not even sure of what one believes is a very common expression such as ’du shes gsum pa and one starts to frantically consult various common dictionaries, only to realize most dictionaries do not even record it. To give an example, the expression ’du shes gsum pa is neither recorded in the Tshig mdzod chen mo nor in the rDa yig gsar bsgrigs. I, of course, do not expect to find it in Jäschke. A shimmer of hope arises when one starts to think of the many dictionaries of enumerations (chos kyi rnam grangs) such as the one by Nor-brang. One does find ’du shes rnam pa gsum but these are Abhidharmic and Yogācāric terms, and not the one you are looking for. And you try to google and that would lead you to Dan Martin’s reference to Śāntideva (who is nicknamed ’Du-shes-gsum-pa’i-zhabs). But what exactly are ’du shes gsum in this name? Your heart starts to skip when you see online dictionaries and resources mentioning ’du shes gsum pa but soon your heart starts to sink with disappointment, when you see these online sources do not take you a single step further. You try to search the TBRC and lo you finally see that one source does mention the kind of ’du shes gsum pa that you are looking for but unfortunately it is like seeing only a fraction of a cake that you can neither have it nor eat it. But fortunately, I discover that I have the cake already. The cake I am talking of is dGe-bshes Thub-bstan-bsam-grub’s mDo sngags tshig mdzod (p. 354). So ’du shes gsum here refers to “three notions” of “eating, sleeping, and going” (za nyal ’gro gsum). I have anticipated along this line but za nyal ’gro ’dug kept on popping up in my mind, which would have been four instead of three. Thus as a bahuvrīhi compound, we could render ’du shes gsum pa as “one who is characterized by three notions (i.e. of eating, sleeping, and going).” It is used by Tibetan authors as a “humilitive” (khengs pa skyungs pa’i tshig). Śāntideva’s nickname Bhu-su-ku is said to be an acronym formed by three Sanskrit words (i.e. bhukta, suptaka, and kuc?). Cf. mDo sngags tshig mdzod (p. 354: bhu ka ta, su ka ta, and ku tstsha ba).
For ’du shes gsum as a Tantric technical term, see the mDo sngags tshig mdzod (p. 354). I have a note made in mKhan-po dBang-phyug-bsod-nams’s class (1987): (1) yab yum lha’i ’du shes, (2) kha gsang rdo rje dang padma’i ’du shes, (3) bde ba chos kyi ’du shes.